Re: Value or Reference Semantics Trait
On Sunday, 12 January 2014 at 20:16:15 UTC, Nordlöw wrote: Is there a trait to check whether a type has value or reference semantics? I need this in a template struct that adaptively (using static if) represent histogram bins as either a dense static array or a sparse associative array. No, afaik. However, the question goes deeper than you might have though. You probably want to distuingish between structs+scalars vs classes. However, what about ref-arguments? Mutable arrays are struct values, but have reference semantics. Immutable-value arrays (e.g. string) have value semantics. You could use one version as default and define special cases via some stuff you find in std.traits.
Re: Value or Reference Semantics Trait
On Sunday, 12 January 2014 at 20:16:15 UTC, Nordlöw wrote: Is there a trait to check whether a type has value or reference semantics? I need this in a template struct that adaptively (using static if) represent histogram bins as either a dense static array or a sparse associative array. That's a complicated question in D. Only simple cases fit one or the other exactly. E.g. A class always has reference semantics, but may contain any combination of reference and value semantic fields. A struct has value semantics, but may contain any combination of reference and value semantic fields. A slice has value semantics w.r.t. its length and start point, but reference semantics for its data. A static array has value semantics. For your problem you should look at the set of IsSomething traits in the table at the top of http://dlang.org/phobos-prerelease/std_traits.html as they will hopefully be sufficient.
Re: Value or Reference Semantics Trait
On Sunday, 12 January 2014 at 20:16:15 UTC, Nordlöw wrote: Is there a trait to check whether a type has value or reference semantics? I need this in a template struct that adaptively (using static if) represent histogram bins as either a dense static array or a sparse associative array. Adding to the other answers: std.traits.hasIndirections
Re: Value or Reference Semantics Trait
If you just want to check if specifically it's a structure, you could always check `__traits(compiles, T()) if(typeof(T()) == T)` beware however that this will evaluate to true if T is a class with a static opCall who's return type is T. On 1/13/14, Tobias Pankrath tob...@pankrath.net wrote: On Sunday, 12 January 2014 at 20:16:15 UTC, Nordlöw wrote: Is there a trait to check whether a type has value or reference semantics? I need this in a template struct that adaptively (using static if) represent histogram bins as either a dense static array or a sparse associative array. Adding to the other answers: std.traits.hasIndirections
Re: Value or Reference Semantics Trait
On Monday, 13 January 2014 at 13:41:30 UTC, Orvid King wrote: If you just want to check if specifically it's a structure, you could always check `__traits(compiles, T()) if(typeof(T()) == T)` beware however that this will evaluate to true if T is a class with a static opCall who's return type is T. is(T == struct)
Re: Value or Reference Semantics Trait
On Monday, 13 January 2014 at 13:41:30 UTC, Orvid King wrote: If you just want to check if specifically it's a structure, you could always check `__traits(compiles, T()) if(typeof(T()) == T)` beware however that this will evaluate to true if T is a class with a static opCall who's return type is T. is(T == struct)
Re: Value or Reference Semantics Trait
On 1/13/14, anonymous anonym...@example.com wrote: On Monday, 13 January 2014 at 13:41:30 UTC, Orvid King wrote: If you just want to check if specifically it's a structure, you could always check `__traits(compiles, T()) if(typeof(T()) == T)` beware however that this will evaluate to true if T is a class with a static opCall who's return type is T. is(T == struct) Or that, yeah XD (For some reason I was thinking about ensuring that it was constructible, which, after reading the question again, isn't actually needed, woops :D) With that in mind, value type semantics would be `enum hasValueSemantics(T) = is(T == struct) || is(T == enum) || is(T == union) || isArray!T;` Be aware however that this assumes you want arrays to be considered to have value semantics due to their length and base element being by-value.
Value or Reference Semantics Trait
Is there a trait to check whether a type has value or reference semantics? I need this in a template struct that adaptively (using static if) represent histogram bins as either a dense static array or a sparse associative array.
