Can I print function type in Swift?

Swift 3 and later

As of Swift 3, __FUNCTION__ is deprecated. Instead, use #function in place of __FUNCTION__.

(Thank you, @jovit.royeca.)

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Swift 2.2 and earlier

You have a few options:

1. print(__FUNCTION__) will output functionName() if the function has no arguments.
2. print(__FUNCTION__) will output functionName (without parentheses) if the function has one or more arguments.

3. print(functionName.dynamicType) will output (() -> Swift.Int) -> Swift.Int for this hypothetical function:

   func functionName(closure: () -> Int) -> Int {
   
   }
   

Thus, to implement the desired functionality for your printType function, you could use a combination of Option 2 and Option 3.

Swift 3 has an interesting new print which prints the type of anything you feed it. It basically prints the same info that is contained in the Code Completion.

print(type(of: functionName())) // prints the return type of a function
// Array<Float>

Here is a convolution method from the Accelerate framework with some properties.

vDSP_conv(newXin, 1, kernel.reversed(), 1, &res, 1, vDSP_Length(T), vDSP_Length(N))

print(type(of: vDSP_conv)) // prints the method arguments.
// ((UnsafePointer<Float>, Int, UnsafePointer<Float>, Int, UnsafeMutablePointer<Float>, Int, UInt, UInt)) -> ()

print(type(of: kernel)) // prints the property type.
// Array<Float>

print(type(of: kernel.reversed())) // prints the property type and method type from the Swift Standard Library.
// ReversedRandomAccessCollection<Array<Float>>

Cool stuff!