new file for constexpr lambdas

Author: Michael Blome

docs/cpp/lambda-expressions-constexpr.md

@@ -0,0 +1,62 @@
+---
+title: "constexpr Lambda Expressions in C++ | Microsoft Docs"
+ms.custom: ""
+ms.date: "07/19/2017"
+ms.reviewer: ""
+ms.suite: ""
+ms.technology:  
+  - "cpp-language"
+ms.tgt_pltfrm: ""
+ms.topic: "language-reference"
+dev_langs: 
+  - "C++"
+helpviewer_keywords: 
+  - "lambda expressions [C++], constexpr"
+ms.assetid: b56346cd-fbff-475f-aeaa-ed2010c6d6f7
+caps.latest.revision: 0
+author: "mikeblome"
+ms.author: "mblome"
+manager: "ghogen"
+---
+# constexpr Lambda Expressions in C++
+In Visual Studio 2017 version 15.3 and later, a lambda expression may be declared as `constexpr` or used in a contant expression when the initialization of each data member that it captures or introduces is allowed within a constant expression.  
+
+```cpp
+    int y = 32;
+	auto answer = [y]() constexpr 
+	{
+		int x = 10;
+		return y + x; 
+	};
+
+    constexpr int Increment(int n) 
+    {
+	    return [n] { return n + 1; }();
+    }
+
+``` 
+A lambda is implicitly `constexpr` if its result satisfies the requirements of a `constexpr` function:
+```cpp
+	auto answer = [](int n) 
+	{
+		return 32 + n; 
+	};
+
+	constexpr int response = answer(10);
+``` 
+If a lambda is implicitly or explicitly `constexpr`, and you convert it to a function pointer, the resulting function is also `constexpr`:
+
+```cpp
+	auto Increment = [](int n)
+	{
+		return n + 1;
+	};
+
+	constexpr int(*inc)(int) = Increment;
+```
+  
+## See Also  
+ [C++ Language Reference](../cpp/cpp-language-reference.md)   
+ [Function Objects in the C++ Standard Library](../standard-library/function-objects-in-the-stl.md)   
+ [Function Call](../cpp/function-call-cpp.md)   
+ [for_each](../standard-library/algorithm-functions.md#for_each)