C++ 17 Test Case Update: Constexpr Lambda

[bigfoot1144]

SrcML does not currently include test cases for C++ 17's Constexpr Lambda

Example

<using>using <name>F</name> <init>= <type><function_decl><type><name>ret</name></type>(<modifier>*</modifier>)<parameter_list>(<parameter><decl><type><name>params</name></type></decl></parameter>)</parameter_list>;</function_decl></type></init></using>
<function_decl type="operator"><name>operator <name>F</name></name><parameter_list>()</parameter_list> <specifier>const</specifier> <noexcept>noexcept</noexcept>;</function_decl>