Reimplement style values atop NSExpression (#10726)

* [ios, macos] Import headers, not implementation files

* [core] Added accessors for various expression parameters

Added missing parameter accessors to various expression operator classes, as well as a method on InterpolatorBase and Step that enumerates the stops and their values.

* [ios, macos] Silenced warning in test of error condition

* [ios, macos] Made MGLSphericalPosition boxable

* [ios, macos] Implemented array enumeration during conversion

* [ios, macos] Temporarily ignore heatmap layer type

* [ios, macos] Migrated MGLSymbolStyleLayer.text to NSExpression

MGLSymbolStyleLayer.text is now of type NSExpression instead of MGLStyleValue, as a first step toward migrating the entire layer API from style values to expressions.

Implemented conversions from NSExpression to JSON arrays and vice versa. The most common NSExpression functions are now converted into style expressions, but not all of the most common style expression operators are supported yet.

* [ios, macos] Implemented string coercion

* [ios, macos] Color literals

* [ios, macos] Null constant expressions

* [ios, macos] Convert dictionary literals

* [ios, macos] Interpolation expressions

* [ios, macos] to-boolean, to-number, get from object

* [ios, macos] Variable expressions

Implemented custom expression functions for assigning and referring to variables within the context of an expression. Variables are assigned via a “context dictionary” and applied to an subexpression that is given as another argument to the same expression. Also implemented built-in variable expressions for zoom level and heatmap density.

* [ios, macos] Convert colors, offsets, padding in expressions to JSON objects

* [ios, macos] Expression-based style property getters

Implemented a conversion from mbgl::style::PropertyValues to Objective-C JSON objects, which are then converted to NSExpressions.

* [ios, macos] Consolidated property value–expression conversion in MGLStyleValueTransformer

* [ios, macos] Predicate and expression guide

Extracted documentation about predicates from a documentation comment in MGLVectorStyleLayer.h to a new jazzy guide. Added details about NSExpression support as well. Began updating the “For Style Authors” guide to reflect the transition from style values to expressions.

* [ios, macos] Updated style authoring guide

Updated the Information for Style Authors guide to discuss expressions instead of style functions. Included a table mapping style specification expression operators to NSExpression syntaxes.

* [ios, macos] Migrated codegen templates to expressions

* [ios, macos] Applied expression changes via codegen

Ran make darwin-style-code.

* [macos] Migrated macosapp to expressions

* [ios, macos] Updated style function guide

This guide needs to be thoroughly rewritten, but for now the example code has been migrated to expressions.

* [ios, macos] Eviscerated style function tests

* [ios, macos] Updated changelogs

* [ios] Migrated iosapp to expressions

* [ios, macos] Exposed JSON conversion methods publicly

* [ios, macos] Removed MGLStyleValue, MGLStyleFunction

1 files changed, 456 insertions, 3 deletions

diff --git a/platform/darwin/test/MGLExpressionTests.mm b/platform/darwin/test/MGLExpressionTests.mm
index ad0833a068..821c5dbdb4 100644
--- a/platform/darwin/test/MGLExpressionTests.mm
+++ b/platform/darwin/test/MGLExpressionTests.mm
@@ -1,9 +1,17 @@
 #import <XCTest/XCTest.h>
 
+#import "MGLStyleLayerTests.h"
+
 #import <string>
 
 #import "MGLTypes.h"
-#import "NSExpression+MGLAdditions.h"
+#import "NSExpression+MGLPrivateAdditions.h"
+#import "NSValue+MGLAdditions.h"
+#if TARGET_OS_IPHONE
+#import "UIColor+MGLAdditions.h"
+#else
+#import "NSColor+MGLAdditions.h"
+#endif
 
 #define MGLAssertEqualValues(actual, expected, ...) \
     XCTAssertTrue(actual.is<__typeof__(expected)>()); \
@@ -17,11 +25,14 @@
         XCTAssertEqualWithAccuracy(actual.get<__typeof__(expected)>(), expected, accuracy, __VA_ARGS__); \
     }
 
+#define MGLConstantExpression(constant) \
+    [NSExpression expressionForConstantValue:constant]
+
 #define MGLAssertConstantEqualsValue(constant, value, ...) \
-    MGLAssertEqualValues([NSExpression expressionForConstantValue:constant].mgl_constantMBGLValue, value, __VA_ARGS__);
+    MGLAssertEqualValues(MGLConstantExpression(constant).mgl_constantMBGLValue, value, __VA_ARGS__);
 
 #define MGLAssertConstantEqualsValueWithAccuracy(constant, value, accuracy, ...) \
-    MGLAssertEqualValuesWithAccuracy([NSExpression expressionForConstantValue:constant].mgl_constantMBGLValue, value, accuracy, __VA_ARGS__);
+    MGLAssertEqualValuesWithAccuracy(MGLConstantExpression(constant).mgl_constantMBGLValue, value, accuracy, __VA_ARGS__);
 
 using namespace std::string_literals;
 
@@ -140,4 +151,446 @@ using namespace std::string_literals;
     XCTAssertEqual([NSExpression expressionForConstantValue:nil].mgl_featureType, mbgl::FeatureType::Unknown);
 }
 
+#pragma mark - JSON expression object tests
+
+- (void)testVariableExpressionObject {
+    {
+        NSExpression *expression = [NSExpression expressionForVariable:@"zoomLevel"];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, @[@"zoom"]);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"$zoomLevel"].mgl_jsonExpressionObject, @[@"zoom"]);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:@[@"zoom"]], expression);
+        NSMutableDictionary *context = [@{@"zoomLevel": @16} mutableCopy];
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:context], @16);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForVariable:@"heatmapDensity"];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, @[@"heatmap-density"]);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"$heatmapDensity"].mgl_jsonExpressionObject, @[@"heatmap-density"]);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:@[@"heatmap-density"]], expression);
+        NSMutableDictionary *context = [@{@"heatmapDensity": @1} mutableCopy];
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:context], @1);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForVariable:@"loremIpsum"];
+        NSArray *jsonExpression = @[@"var", @"loremIpsum"];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"$loremIpsum"].mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+        NSMutableDictionary *context = [@{@"loremIpsum": @"Lorem ipsum dolor sit amet"} mutableCopy];
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:context], @"Lorem ipsum dolor sit amet");
+    }
+    {
+        NSDictionary *context = @{@"loremIpsum": MGLConstantExpression(@"Lorem ipsum dolor sit amet")};
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(uppercase($loremIpsum), 'mgl_expressionWithContext:', %@)", context];
+        NSArray *jsonExpression = @[@"let", @"loremIpsum", @"Lorem ipsum dolor sit amet", @[@"upcase", @[@"var", @"loremIpsum"]]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+}
+
+- (void)testConstantValueExpressionObject {
+    {
+        NSExpression *expression = [NSExpression expressionForConstantValue:nil];
+        XCTAssert(expression.mgl_jsonExpressionObject == [NSNull null]);
+        XCTAssert([NSExpression expressionWithFormat:@"nil"].mgl_jsonExpressionObject == [NSNull null]);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:[NSNull null]], expression);
+        XCTAssertNil([expression expressionValueWithObject:nil context:nil]);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForConstantValue:@1];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, @1);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"1"].mgl_jsonExpressionObject, @1);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:@1], expression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @1);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForConstantValue:@YES];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, @YES);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"TRUE"].mgl_jsonExpressionObject, @YES);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:@YES], expression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @YES);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForConstantValue:nil];
+        XCTAssert(expression.mgl_jsonExpressionObject == [NSNull null]);
+        XCTAssert([NSExpression expressionWithFormat:@"nil"].mgl_jsonExpressionObject == [NSNull null]);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:[NSNull null]], expression);
+        XCTAssertNil([expression expressionValueWithObject:nil context:nil]);
+    }
+    {
+        CGVector vector = CGVectorMake(1, 2);
+        NSExpression *expression = [NSExpression expressionForConstantValue:@(vector)];
+#if !TARGET_OS_IPHONE
+        NSArray *jsonExpression = @[@"literal", @[@1, @-2]];
+#else
+        NSArray *jsonExpression = @[@"literal", @[@1, @2]];
+#endif
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        // No way to distinguish offsets from ordinary arrays in expressions.
+        XCTAssertEqualObjects([[NSExpression mgl_expressionWithJSONObject:jsonExpression].collection valueForKeyPath:@"constantValue"], jsonExpression.lastObject);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @(vector));
+    }
+    {
+#if !TARGET_OS_IPHONE
+        NSEdgeInsets padding = {1, 2, 3, 4};
+        NSValue *value = [NSValue valueWithEdgeInsets:padding];
+#else
+        UIEdgeInsets padding = {1, 2, 3, 4};
+        NSValue *value = [NSValue valueWithUIEdgeInsets:padding];
+#endif
+        NSExpression *expression = [NSExpression expressionForConstantValue:value];
+        NSArray *jsonExpression = @[@"literal", @[@1, @4, @3, @2]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        // No way to distinguish offsets from ordinary arrays in expressions.
+        XCTAssertEqualObjects([[NSExpression mgl_expressionWithJSONObject:jsonExpression].collection valueForKeyPath:@"constantValue"], jsonExpression.lastObject);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], value);
+    }
+    {
+        MGLColor *color = [MGLColor mgl_colorWithColor:{ 255.0/255, 239.0/255, 213.0/255, 1 }]; // papayawhip
+        NSExpression *expression = [NSExpression expressionForConstantValue:color];
+        NSArray *jsonExpression = @[@"rgb", @255, @239, @213];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], color);
+    }
+    {
+        MGLColor *color = [MGLColor mgl_colorWithColor:{ 255.0/255, 239.0/255, 213.0/255, 0.5 }]; // papayawhip
+        NSExpression *expression = [NSExpression expressionForConstantValue:color];
+        NSArray *jsonExpression = @[@"rgba", @255, @239, @213, @0.5];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], color);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"noindex(513)"];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, @513);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @513);
+    }
+}
+
+- (void)testKeyPathExpressionObject {
+    {
+        NSExpression *expression = [NSExpression expressionForKeyPath:@"highway"];
+        NSArray *jsonExpression = @[@"get", @"highway"];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"highway"].mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"%@.population", @{@"population": MGLConstantExpression(@12000)}];
+        NSArray *jsonExpression = @[@"get", @"population", @[@"literal", @{@"population": @12000}]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"%@.uppercase('population')", @{@"POPULATION": MGLConstantExpression(@12000)}];
+        NSArray *jsonExpression = @[@"get", @[@"upcase", @"population"], @[@"literal", @{@"POPULATION": @12000}]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+}
+
+- (void)testStatisticalExpressionObject {
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"average({1, 2, 2, 3, 4, 7, 9})"];
+        NSArray *jsonExpression = @[@"/", @[@"+", @1, @2, @2, @3, @4, @7, @9], @[@"length", @[@"literal", @[@1, @2, @2, @3, @4, @7, @9]]]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @4);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"sum({1, 2, 2, 3, 4, 7, 9})"];
+        NSArray *jsonExpression = @[@"+", @1, @2, @2, @3, @4, @7, @9];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @28);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"count({1, 2, 2, 3, 4, 7, 9})"];
+        NSArray *jsonExpression = @[@"length", @[@"literal", @[@1, @2, @2, @3, @4, @7, @9]]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @7);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"min({1, 2, 2, 3, 4, 7, 9})"];
+        NSArray *jsonExpression = @[@"min", @1, @2, @2, @3, @4, @7, @9];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @1);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"max({1, 2, 2, 3, 4, 7, 9})"];
+        NSArray *jsonExpression = @[@"max", @1, @2, @2, @3, @4, @7, @9];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @9);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+}
+
+- (void)testArithmeticExpressionObject {
+    NSArray *arguments = @[MGLConstantExpression(@1), MGLConstantExpression(@1)];
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"add:to:" arguments:arguments];
+        NSArray *jsonExpression = @[@"+", @1, @1];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"1 + 1"].mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"from:subtract:" arguments:arguments];
+        NSArray *jsonExpression = @[@"-", @1, @1];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"1 - 1"].mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"multiply:by:" arguments:arguments];
+        NSArray *jsonExpression = @[@"*", @1, @1];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"1 * 1"].mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"divide:by:" arguments:arguments];
+        NSArray *jsonExpression = @[@"/", @1, @1];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"1 / 1"].mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"modulus:by:" arguments:arguments];
+        NSArray *jsonExpression = @[@"%", @1, @1];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        // NSExpression lacks a shorthand operator for modulus.
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"ceiling:" arguments:@[MGLConstantExpression(@1.5)]];
+        NSArray *jsonTruncation = @[@"-", @1.5, @[@"%", @1.5, @1]];
+        NSArray *jsonExpression = @[@"+", jsonTruncation, @[@"case", @[@">", @[@"%", @1.5, @1], @0], @1, @0]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @2);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"ceiling:" arguments:@[MGLConstantExpression(@-1.5)]];
+        NSArray *jsonTruncation = @[@"-", @-1.5, @[@"%", @-1.5, @1]];
+        NSArray *jsonExpression = @[@"+", jsonTruncation, @[@"case", @[@">", @[@"%", @-1.5, @1], @0], @1, @0]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @-1);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"ceiling:" arguments:@[MGLConstantExpression(@2)]];
+        NSArray *jsonTruncation = @[@"-", @2, @[@"%", @2, @1]];
+        NSArray *jsonExpression = @[@"+", jsonTruncation, @[@"case", @[@">", @[@"%", @2, @1], @0], @1, @0]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @2);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"ceiling:" arguments:@[MGLConstantExpression(@-2)]];
+        NSArray *jsonTruncation = @[@"-", @-2, @[@"%", @-2, @1]];
+        NSArray *jsonExpression = @[@"+", jsonTruncation, @[@"case", @[@">", @[@"%", @-2, @1], @0], @1, @0]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @-2);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"trunc:" arguments:@[MGLConstantExpression(@1.5)]];
+        NSArray *jsonExpression = @[@"-", @1.5, @[@"%", @1.5, @1]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @1);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"trunc:" arguments:@[MGLConstantExpression(@-1.5)]];
+        NSArray *jsonExpression = @[@"-", @-1.5, @[@"%", @-1.5, @1]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @-1);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"abs:" arguments:@[MGLConstantExpression(@2)]];
+        NSArray *jsonExpression = @[@"*", @2, @[@"case", @[@">", @2, @0], @1, @-1]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @2);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"abs:" arguments:@[MGLConstantExpression(@-2)]];
+        NSArray *jsonExpression = @[@"*", @-2, @[@"case", @[@">", @-2, @0], @1, @-1]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @2);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"floor:" arguments:@[MGLConstantExpression(@1.5)]];
+        NSArray *jsonTruncation = @[@"-", @1.5, @[@"%", @1.5, @1]];
+        NSArray *jsonExpression = @[@"-", jsonTruncation, @[@"case", @[@"<", @[@"%", @1.5, @1], @0], @1, @0]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @1);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"floor:" arguments:@[MGLConstantExpression(@-1.5)]];
+        NSArray *jsonTruncation = @[@"-", @-1.5, @[@"%", @-1.5, @1]];
+        NSArray *jsonExpression = @[@"-", jsonTruncation, @[@"case", @[@"<", @[@"%", @-1.5, @1], @0], @1, @0]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @-2);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"floor:" arguments:@[MGLConstantExpression(@2)]];
+        NSArray *jsonTruncation = @[@"-", @2, @[@"%", @2, @1]];
+        NSArray *jsonExpression = @[@"-", jsonTruncation, @[@"case", @[@"<", @[@"%", @2, @1], @0], @1, @0]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @2);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"floor:" arguments:@[MGLConstantExpression(@-2)]];
+        NSArray *jsonTruncation = @[@"-", @-2, @[@"%", @-2, @1]];
+        NSArray *jsonExpression = @[@"-", jsonTruncation, @[@"case", @[@"<", @[@"%", @-2, @1], @0], @1, @0]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @-2);
+    }
+}
+
+- (void)testTrigonometricExpressionObject {
+    NSArray *arguments = @[MGLConstantExpression(@1), MGLConstantExpression(@1)];
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"sqrt:" arguments:arguments];
+        NSArray *jsonExpression = @[@"sqrt", @1, @1];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"ln:" arguments:arguments];
+        NSArray *jsonExpression = @[@"ln", @1, @1];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"raise:toPower:" arguments:arguments];
+        NSArray *jsonExpression = @[@"^", @1, @1];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"1 ** 1"].mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"exp:" arguments:@[MGLConstantExpression(@0)]];
+        NSArray *jsonExpression = @[@"^", @[@"e"], @0];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @1);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForConstantValue:@(M_E)];
+        NSArray *jsonExpression = @[@"e"];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @(M_E));
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForConstantValue:@(M_PI)];
+        NSArray *jsonExpression = @[@"pi"];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @(M_PI));
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+}
+
+- (void)testStringFormattingExpressionObject {
+    NSArray *arguments = @[MGLConstantExpression(@"MacDonald")];
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION('Old', 'stringByAppendingString:', 'MacDonald')"];
+        NSArray *jsonExpression = @[@"concat", @"Old", @"MacDonald"];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @"OldMacDonald");
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"uppercase:" arguments:arguments];
+        NSArray *jsonExpression = @[@"upcase", @"MacDonald"];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"lowercase:" arguments:arguments];
+        NSArray *jsonExpression = @[@"downcase", @"MacDonald"];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+}
+
+- (void)testTypeConversionExpressionObject {
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(number, 'boolValue')"];
+        NSArray *jsonExpression = @[@"to-boolean", @[@"get", @"number"]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        // NSExpression is unable to evaluate -[NSNumber boolValue] by itself
+        // because it returns a primitive instead of an object.
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(postalCode, 'mgl_numberWithFallbackValues:', zipCode)"];
+        NSArray *jsonExpression = @[@"to-number", @[@"get", @"postalCode"], @[@"get", @"zipCode"]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"FUNCTION(postalCode, 'doubleValue', zipCode)"].mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"FUNCTION(postalCode, 'floatValue', zipCode)"].mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"FUNCTION(postalCode, 'decimalValue', zipCode)"].mgl_jsonExpressionObject, jsonExpression);
+        // NSExpression is unable to evaluate NSNumber’s -floatValue,
+        // -doubleValue, or -decimalValue by themselves because they each return
+        // a primitive instead of an object.
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(number, 'stringValue')"];
+        NSArray *jsonExpression = @[@"to-string", @[@"get", @"number"]];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:@{@"number": @1.5} context:nil], @"1.5");
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+}
+
+- (void)testInterpolationExpressionObject {
+    {
+        NSDictionary *stops = @{@0: MGLConstantExpression(@100), @10: MGLConstantExpression(@200)};
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(x, 'mgl_interpolateWithCurveType:parameters:stops:', 'linear', nil, %@)", stops];
+        NSArray *jsonExpression = @[@"interpolate", @[@"linear"], @[@"get", @"x"], @0, @100, @10, @200];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSDictionary *stops = @{@1: MGLConstantExpression(@2), @3: MGLConstantExpression(@6)};
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(x, 'mgl_interpolateWithCurveType:parameters:stops:', 'exponential', 2, %@)", stops];
+        NSArray *jsonExpression = @[@"interpolate", @[@"exponential", @2], @[@"get", @"x"], @1, @2, @3, @6];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSDictionary *stops = @{@0: MGLConstantExpression(@0), @100: MGLConstantExpression(@100)};
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(x, 'mgl_interpolateWithCurveType:parameters:stops:', 'cubic-bezier', { 0.42, 0, 0.58, 1 }, %@)", stops];
+        NSArray *jsonExpression = @[@"interpolate", @[@"cubic-bezier", @0.42, @0, @0.58, @1], @[@"get", @"x"], @0, @0, @100, @100];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSDictionary *stops = @{@0: MGLConstantExpression(@111), @1: MGLConstantExpression(@1111)};
+        NSExpression *expression = [NSExpression expressionWithFormat:@"FUNCTION(x, 'mgl_stepWithMinimum:stops:', 11, %@)", stops];
+        NSArray *jsonExpression = @[@"step", @[@"get", @"x"], @11, @0, @111, @1, @1111];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+}
+
+- (void)testConditionalExpressionObject {
+    {
+        NSPredicate *conditional = [NSPredicate predicateWithFormat:@"1 = 2"];
+        NSExpression *trueExpression = [NSExpression expressionForConstantValue:@YES];
+        NSExpression *falseExpression = [NSExpression expressionForConstantValue:@NO];
+        NSExpression *expression = [NSExpression expressionForConditional:conditional trueExpression:trueExpression falseExpression:falseExpression];
+        NSArray *jsonExpression = @[@"case", @[@"==", @1, @2], @YES, @NO];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([NSExpression expressionWithFormat:@"TERNARY(1 = 2, TRUE, FALSE)"].mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @NO);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+    {
+        NSExpression *expression = [NSExpression expressionWithFormat:@"TERNARY(0 = 1, TRUE, TERNARY(1 = 2, TRUE, FALSE))"];
+        NSArray *jsonExpression = @[@"case", @[@"==", @0, @1], @YES, @[@"==", @1, @2], @YES, @NO];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @NO);
+        XCTAssertEqualObjects([NSExpression mgl_expressionWithJSONObject:jsonExpression], expression);
+    }
+}
+
 @end