[swift-evolution] [Discussion] Seal `T.Type` into `Type<T>`

[Adrian Zubarev]

Changed the implementation to this:

public var size: Int { return _sizeof(self._metatype) }
public var stride: Int { return _strideof(self._metatype) }
public var alignment: Int { return _alignof(self._metatype) }
     
public static var size: Int { return _sizeof(T.metatype) }
public static var stride: Int { return _strideof(T.metatype) }
public static var alignment: Int { return _alignof(T.metatype) }
Where the internal functions are based on current swift implementation except that instead of T.Type it would be better to use AnyMetatype.

internal func _sizeof(_ metatype: AnyMetatype) -> Int {
    return Int(Builtin.sizeof(metatype))
}

internal func _strideof(_ metatype: AnyMetatype) -> Int {
    return Int(Builtin.strideof_nonzero(metatype))
}

internal func _alignof(_ metatype: AnyMetatype) -> Int {
    return Int(Builtin.alignof(metatype))
}
I can’t test this because current sizeof, strideof and alignof are using T.Type where something like this doesn’t work:

sizeof(Int.self) // 8
sizeof(CustomStringConvertible.self) // 40

sizeof(Int.self as CustomStringConvertible.Type) // Error
That said I can only assume that the buildin function will return the correct value for the provided metatype.

let x = Int // equals Type<Int>.sharedInstance
x.size // 8

let y = Type<CustomStringConvertible>.cast(x)
y?.size // should be 8 as well
size and alignment would work analogically.

Type<T>.size // always returns the size of T


-- 
Adrian Zubarev
Sent with Airmail

Am 15. Juli 2016 um 19:05:56, Anton Zhilin (antonyzhilin at gmail.com) schrieb:

Next, I’d like to remind you of my 
size, 
stride, 
align concerns. Consider this example:

let x = Type<Int>()
let y = Type<CustomStringConvertible>(casting: x)!
x.size  //=> 8
y.size  //=> 8 or 40?
I think that 
y.size should be 8, because we are dynamically checking size of particular instance 
y, which refers to specific subtype of 
CustomStringConvertible. 

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