Generic Lambdas (C++14)

In a Nutshell

Lets lambda expression parameters take auto, sparing us the hassle of writing multiple overloads for different types — it is equivalent to generating a templated operator().

Header

None (language feature)

Core API Quick Reference

Operation	Signature	Description
Generic parameters	[captures](auto a, auto b) { ... }	Declare parameters with auto; a templated operator() is generated from the deduced types
Forwarding reference parameters	[captures](auto&&... ts) { ... }	Combine auto&& with perfect forwarding of the parameter pack
Explicit template parameters (C++20)	[captures]<class T>(T a) { ... }	Declare template parameters explicitly in angle brackets after the square brackets; supports constraints
No-capture function pointer conversion	using F = ret(*)(params); operator F() const;	Capture-less generic lambdas convert implicitly to a function pointer (constexpr since C++17)

Minimal Example

#include <iostream>
// Standard: C++14
int main() {
    auto compare = [](auto a, auto b) { return a < b; };
    std::cout << compare(3, 4) << "\n";       // int vs int
    std::cout << compare(3.14, 2.72) << "\n"; // double vs double
}

Embedded Suitability: High

• Zero runtime overhead: auto is deduced purely at compile time, and the generated code is identical to a hand-written template
• A great fit for generic callbacks (sorting comparators, timer callbacks, and the like), cutting down template code redundancy
• The C++14 auto syntax is already widely supported by GCC 5+ / Clang 3.4+, so every mainstream embedded toolchain can use it

Compiler Support

GCC	Clang	MSVC
5.0	3.4	19.0

See Also

• cppreference: Lambda expressions

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