[Bridge] RCT_REMAP_METHOD(js_name, selector)

[ide]

cc @a2 @nicklockwood

This diff introduces a new macro called RCT_EXPORT_NAMED_METHOD, which is like RCT_EXPORT_METHOD but lets you choose the name of the method in JS. This diff is backwards compatible with the RCT_EXPORT_METHOD and legacy RCT_EXPORT macros.

The entries in the data segment now contain __func__, the Obj-C selector signature, and the JS name. If the JS name is NULL, we take the legacy RCT_EXPORT code path. If the JS name is an empty string, we use the Obj-C selector's name up to the first colon (that is, the behavior of RCT_EXPORT_METHOD).

Since there are three values in each data segment entry, the macros now specify 1-byte alignment. Without the byte alignment, the compiler defaults to 2-byte alignment meaning that each entry takes up 4 bytes instead of 3. The extra byte isn't a concern but being explicit about the alignment should reduce compiler surprises.

[ide]

If this looks good I'll send another PR to update the docs once this lands.

[nicklockwood]

We did debate adding this at the time of the refactor. In the end I decided it wasn't really necessary - these methods are written explicitly for the purpose of exporting to JavaScript, so there's no need to maintain compatibility with existing code, and the approach of taking just the first part of the selector allows full freedom to name it whatever you want.

The only disadvantage is that it forces you to sometimes name your method slightly un-idiomatically with respect to Objective-C - i.e. you might have to call it:

- (void)doSomething:(id)foo bar:(id)bar;

Instead of:

- (void)doSomethingWithFoo:(id)foo bar:(id)bar;

Which would be the convention. This does bother me a little bit, but honestly so few people will care about this that it hardly seems worth increasing the API surface to support it. We checked our existing modules and there were only about 2 cases in the whole project where someone had bothered to use a different name, even though this was fully supported under the old system.

[nicklockwood]

Another solution I considered was to do the Swift-like thing of removing the WithX: from the first selector, if present. Then you could write

- (void)doSomethingWithFoo:(id)foo bar:(id)bar;

And the JS method would still be. doSomething().

The reason I decided against that is that, while it would make Objective-C people happier, it would cause more confusion for JS developers, and we want to avoid that since the majority of our target audience at the moment are not expert native developers.

[nicklockwood]

Another thought:

For properties, where we do support something similar, we call the macro RCT_REMAP_VIEW_PROPERTY(). I don't love this, but it if we were to add such a feature, I feel we should try to be consistent with the naming.

[ide]

Renaming it to RCT_REMAP_METHOD is alright with me. I had a need for this in a database module where the Obj-C selectors looked like:

- (void)executeQuery:(NSString *)query parameterDictionary:(NSDictionary *)parameters successCallback:...;
- (void)executeQuery:(NSString *)query argumentsArray:(NSArray *)array successCallback:...;

These are exported to JS as executeQueryWithParameters and executeQueryWithArgumentArray respectively. I was much more satisified with named exports than awkwardly writing

- (void)executeQueryWithParameters:(NSString *)query parameterDictionary:(NSDictionary *)parameters successCallback:...

[nicklockwood]

Eh.. fair enough :-)

[ide]

Merged in 862d9fb.