From 6b97f71bd6e25fc9d1aac7987768f56b78fcf24d Mon Sep 17 00:00:00 2001
From: Fabian Guerra <fabian.guerra@mapbox.com>
Date: Tue, 17 Apr 2018 16:15:26 -0400
Subject: [ios, macos] Add tangent NSExpresssion operator.

---
 platform/darwin/src/NSExpression+MGLAdditions.mm | 10 ++++++++++
 platform/darwin/test/MGLExpressionTests.mm       |  7 +++++++
 2 files changed, 17 insertions(+)

diff --git a/platform/darwin/src/NSExpression+MGLAdditions.mm b/platform/darwin/src/NSExpression+MGLAdditions.mm
index 8c79fd43f8..e641c79628 100644
--- a/platform/darwin/src/NSExpression+MGLAdditions.mm
+++ b/platform/darwin/src/NSExpression+MGLAdditions.mm
@@ -73,6 +73,7 @@ const MGLExpressionInterpolationMode MGLExpressionInterpolationModeCubicBezier =
     INSTALL_METHOD(mgl_asin:);
     INSTALL_METHOD(mgl_sin:);
     INSTALL_METHOD(mgl_atan:);
+    INSTALL_METHOD(mgl_tan:);
     
     // Install functions that resemble control structures, taking arbitrary
     // numbers of arguments. Vararg aftermarket functions need to be declared
@@ -137,6 +138,13 @@ const MGLExpressionInterpolationMode MGLExpressionInterpolationModeCubicBezier =
     return @(atan(number.doubleValue));
 }
 
+/**
+ Computes the principal value of the tangent.
+ */
+- (NSNumber *)mgl_tan:(NSNumber *)number {
+    return @(tan(number.doubleValue));
+}
+
 /**
  A placeholder for a method that evaluates an interpolation expression.
  */
@@ -720,6 +728,7 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
             @"asin" : @"mgl_asin:",
             @"sin" : @"mgl_sin:",
             @"atan" : @"mgl_atan:",
+            @"tan" : @"mgl_tan:",
             @"floor": @"floor:",
             @"ceil": @"ceiling:",
             @"^": @"raise:toPower:",
@@ -967,6 +976,7 @@ NSArray *MGLSubexpressionsWithJSONObjects(NSArray *objects) {
             @"mgl_asin:" : @"asin",
             @"mgl_sin:" : @"sin",
             @"mgl_atan:" : @"atan",
+            @"mgl_tan:" : @"tan",
             // Vararg aftermarket expressions need to be declared with an explicit and implicit first argument.
             @"MGL_LET": @"let",
             @"MGL_LET:": @"let",
diff --git a/platform/darwin/test/MGLExpressionTests.mm b/platform/darwin/test/MGLExpressionTests.mm
index 4e18ad694d..864310356c 100644
--- a/platform/darwin/test/MGLExpressionTests.mm
+++ b/platform/darwin/test/MGLExpressionTests.mm
@@ -567,6 +567,13 @@ using namespace std::string_literals;
         XCTAssertEqualWithAccuracy(value.doubleValue, 1.52, 0.001);
         XCTAssertEqualObjects([NSExpression expressionWithMGLJSONObject:jsonExpression], expression);
     }
+    {
+        NSExpression *expression = [NSExpression expressionForFunction:@"mgl_tan:" arguments:@[MGLConstantExpression(@0)]];
+        NSArray *jsonExpression = @[@"tan", @0];
+        XCTAssertEqualObjects(expression.mgl_jsonExpressionObject, jsonExpression);
+        XCTAssertEqualObjects([expression expressionValueWithObject:nil context:nil], @0);
+        XCTAssertEqualObjects([NSExpression expressionWithMGLJSONObject:jsonExpression], expression);
+    }
 }
 
 - (void)testStringFormattingExpressionObject {
-- 
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