Open Radar

 
Summary:
Given how smart the compiler is at helping interoperability when using ObjC API from Swift, I thought I'd suggest the following enhancement.

When writing my own API, part of those contracts is that `nil` is sometimes disallowed as a value for an argument. Apple has encouraged enforcing this by using the NSParameterAssert macro in the first lines inside a method's implementation.

Could it be possible that the compiler can see these assertions, and therefore mark a parameter as non-optional?

Steps to Reproduce:
__Example from NSFileManager Documentation__

Copies the item at the specified path to a new location synchronously.

- (BOOL)copyItemAtPath:(NSString *)srcPath toPath:(NSString *)dstPath error:(NSError **)error

Parameters

**srcPath**
The path to the file or directory you want to move. This parameter must not be nil.

**dstPath**
The path at which to place the copy of srcPath. This path must include the name of the file or directory in its new location. This parameter must not be nil.

**error**
On input, a pointer to an error object. If an error occurs, this pointer is set to an actual error object containing the error information. You may specify nil for this parameter if you do not want the error information.

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When converted to Swift, the method signature looks like this:

func copyItemAtPath(_ srcPath: String!, toPath dstPath: String!, error error: NSErrorPointer) -> Bool

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Of course I'm making an assumption to drive my point, but in the implementation of this method, there should be:

NSParameterAssert(srcPath);
NSParameterAssert(dstPath);

...which could allow Swift to generate a method signature like this:

func copyItemAtPath(_ srcPath: String, toPath dstPath: String, error error: NSErrorPointer) -> Bool

(note lack of exclamation points)

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Apple Developer Relations10-Jun-2014 07:03 PM

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