GCC __attribute__((always_inline)) and lambdas, is this syntax correct?

Question

I am using GCC 4.6 as part of the lpcxpresso ide for a Cortex embedded processor. I have very limited code size, especially when compiling in debug mode. Using attribute((always_inline)) has so far proven to be a good tool to inline trivial functions and this saves a lot of code bloat in debug mode while still maintaining readability. I expect it to be somewhat mainstream and supported in the future because it is mentioned here http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0348c/CIAJGAIH.html

Now to my question: Is this the correct Syntax for declaring a Lambda always inline?

#define ALWAYS_INLINE __attribute__((always_inline))
[](volatile int &i)ALWAYS_INLINE{i++;}

It does work, my question is will it continue to work in future and what can I do to ensure it works in the future. If I ever switch to another major compiler that supports c++11 will I find a similar keyword which I can replace the attribute((always_inline)) with? If I were to meet my fairy godmother I would wish for a compiler directive which causes all lambdas which are constructed as temporaries with empty constructors and bound by reference to be automatically inlined even in debug mode. Any ideas?

Answer 1

Will it continue to work in future?

Likely but, always_inline is compiler specific and since there is no standard specifying its exact behavior with lambda, there is no guaranty that this will continue to work in the future.

What can I do to ensure it works?

This depends on the compiler not you. If a future version drops support for always_inline with lambda, you have to stick with a version that works or code your own preprocessor that inlines lambdas with an always_inline-like keyword.

If I ever switch to another major compiler that supports c++11 will I find a similar keyword?

Likely but again, there is no guaranty. The only real standard is the C++ inline keyword and it is not applicable to lambdas. For non-lambda it only suggests inlining and tells the compiler that a function may be defined in different compile units.