What C++ [[attributes]] are implemented by cheerp?

Question

The C++11 specification defined [[attributes]] which can be used to specify/influence implementation-defined behavior. Cheerp supports this for specifying whether you're writing C++ code meant to be compiled into [[cheerp::genericjs]] or [[cheerp::wasm]] code. This results in your C++ code being compiled into the .js or .wasm output of the compiler respectively. (Right?)

My question: What attributes does Cheerp know and what do they all do?

So far, I've seen the following attributes:

[[cheerp::genericjs]]
[[cheerp::wasm]]
[[cheerp::asmjs]]
[[cheerp::client_layout]]
[[cheerp::static]]
[[cheerp::jsexport]]

Answer 1

The ones that are meant to be used by users are:

• cheerp::genericjs: compile the associated item (class/struct definition, global, or function) to JavaScript, using the object memory model

• cheerp::wasm: compile the associated item (class/struct definition, global, or function) to WebAssembli OR asm.js, using the linear memory model. cheerp::asmjs is an alias of cheerp::wasm and considered obsoleted (but kept for backward compatibility). The actual output (wasm or asm.js) depends on command line flags

• client::jsexport: export the associated item (function or class/struct) so that it can be used from external JavaScript code

The other attributes you mention do exist, but you should almost never use them yourself. Their meaning is this:

• cheerp::static: tell the compiler that the associated method of a client class is static (example: Date.now()). Used in the implementation of various browser apis
• cheerp::client_layout: tell the compiler that this class/struct has an external layout defined in external JavaScript. You never need to use this if you inherit your client classes from client::Object (which you should), because derived classes inherit this attribute