digitalmars.D - How to extract the AA type?
- Steven Schveighoffer (31/31) Dec 13 2017 A nice puzzle for those template gurus out there.
- jmh530 (9/19) Dec 13 2017 [snip]
- Steven Schveighoffer (7/32) Dec 13 2017 Yes, that seems to work, I was worried that something like this would
- Steven Schveighoffer (6/23) Dec 14 2017 After thinking about it, I've decided to simply use the workaround I
- Jack Applegame (6/6) Dec 13 2017 auto foo(T: V[K], V, K)(T t)
A nice puzzle for those template gurus out there. I have a function like this: auto foo(T: V[K], V, K)(T t) { RealAAType!(T, V, K) aa = t; return aa; } So I need to know what to write RealAAType. What I'm looking for is a mechanism to write the exact AA type that is passed in. RealAAType should be an AA, and nothing else. Here are 2 things that *don't* work: alias RealAAType!(T, V, K) = T; This doesn't work because T could be an alias this'd struct. I don't want T, I want the actual AA type. alias RealAAType!(T, V, K) = V[K]; This doesn't work when the T has a type modifier. For instance if T is const(int[int]), then V[K] is really const(int)[int], and you can't assign it to t. Here is are the tests I want to compile: const(int[int]) x; auto aa1 = foo(x); static assert(typeof(aa1) == const(int[int])); static struct S { int[int] aa; alias aa this; } const(S) s; auto aa2 = foo(s); static assert(typeof(aa2) == const(int[int])); -Steve
Dec 13 2017
On Wednesday, 13 December 2017 at 16:00:32 UTC, Steven Schveighoffer wrote:A nice puzzle for those template gurus out there. I have a function like this: auto foo(T: V[K], V, K)(T t) { RealAAType!(T, V, K) aa = t; return aa; } So I need to know what to write RealAAType. What I'm looking for is a mechanism to write the exact AA type that is passed in. RealAAType should be an AA, and nothing else.[snip] How about: template RealAAType!(T, V, K) { import std.traits : CopyConstness; alias RealAAType = CopyConstness!(T, V[K]); }
Dec 13 2017
On 12/13/17 11:30 AM, jmh530 wrote:On Wednesday, 13 December 2017 at 16:00:32 UTC, Steven Schveighoffer wrote:Yes, that seems to work, I was worried that something like this would give me multiple type modifiers (.e.g const(const(int)[int]) Now, I need to figure out how to do this in object.d :) BTW, the PR that spurred this for reference: https://github.com/dlang/druntime/pull/1992 -SteveA nice puzzle for those template gurus out there. I have a function like this: auto foo(T: V[K], V, K)(T t) { RealAAType!(T, V, K) aa = t; return aa; } So I need to know what to write RealAAType. What I'm looking for is a mechanism to write the exact AA type that is passed in. RealAAType should be an AA, and nothing else.[snip] How about: template RealAAType!(T, V, K) { import std.traits : CopyConstness; alias RealAAType = CopyConstness!(T, V[K]); }
Dec 13 2017
On 12/13/17 3:23 PM, Steven Schveighoffer wrote:On 12/13/17 11:30 AM, jmh530 wrote:After thinking about it, I've decided to simply use the workaround I implemented, just apply const to the AA in all cases, since I have to cast to void * anyway. Thanks for the tips, I learned a little bit here :) -SteveHow about: template RealAAType!(T, V, K) { import std.traits : CopyConstness; alias RealAAType = CopyConstness!(T, V[K]); }Yes, that seems to work, I was worried that something like this would give me multiple type modifiers (.e.g const(const(int)[int]) Now, I need to figure out how to do this in object.d :) BTW, the PR that spurred this for reference: https://github.com/dlang/druntime/pull/1992
Dec 14 2017
auto foo(T: V[K], V, K)(T t) { CopyConstness!(T, V[K]) aa = t; return aa; } https://run.dlang.io/is/LSMa5C
Dec 13 2017