> On Nov 16, 2017, at 4:38 PM, Howard Lovatt <howard.lov...@gmail.com> wrote: > > When the user writes: > > let increment: <T>(T) throws -> T where T: Numeric = { $0 + 1 } > increment(1) // 2 > increment(1.1) // 2.1
This means that ‘increment’ is a *value* with a generic function type. Presumably you want to pass generic closures as function parameters and results too. This is called higher-rank polymorphism and it introduces considerable complexity in type checking and code generation. > Compiler issues global struct as above. Then: > > let _int_increment = _Function1__T1__T1__T1__E__Numeric<Int>({ $0 + 1 }) > try _int_increment.call(1) // 2 > let _double_increment = _Function1__T1__T1__T1__E__Numeric<Double>({ $0 + > 1 }) > try _double_increment.call(1.1) // 2.1 What if I do, let array = [increment] What is the type of ‘array’? Slava > > The more restrictive form that you suggest (I think this is what you mean > anyway) of only allowed locally, not globally, is easier to name mangle, you > just need a unique name, nothing about the name needs to be canonical. This > would be similar to local functions at present and would be useful (though I > am not sure how many local *generic* functions there are). > > > -- Howard. > > On 17 November 2017 at 10:47, Slava Pestov <spes...@apple.com > <mailto:spes...@apple.com>> wrote: > > >> On Nov 16, 2017, at 3:07 PM, Howard Lovatt via swift-evolution >> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote: >> >> Where I am proposing a change is that if a closure with generic arguments is >> encountered it is transformed into the equivalent struct and the struct is >> typed as it currently is (or if there is a better implementation something >> equivalent to this), therefore zero change to the type system. > > Since we already have local functions that can capture values and be generic, > there’s no need to implement a new mechanism for name mangling or handling of > captures. > >> >> The changes proposed are a transformation into a struct and name mangling, >> e.g.: >> >> let increment: <T>(T) throws -> T where T: Numeric = { $0 + 1 } >> let increment = { <T>(n: T) throws -> T where T: Numeric in n + 1 } >> let increment: <T>(T) throws -> T where T: Numeric = { <T>(n: T) throws >> -> T where T: Numeric in n + 1 } > > It sounds like what you’re proposing is essentially a new surface syntax for > local functions — since a generic closure would not be a first class value, > it could not appear anywhere except for the right hand side of a let binding, > right? > > Slava >
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