• Tony (9/9) Feb 18 2018 At
• Mike Parker (19/28) Feb 18 2018 Generally, no. But with alias this, it can be:
• Tony (7/24) Feb 19 2018 Thanks!
• Basile B. (4/9) Feb 19 2018 Indeed but Phobos maintainers don't want the ...TypeOf family to
• Tony (6/9) Feb 19 2018 Ok, thanks.
• Nathan S. (2/6) Feb 19 2018 In that case you can just write `is(T : bool)`.
• Tony (7/13) Feb 19 2018 Thanks.

Tony <tonytdominguez aol.com> writes:

At
https://dlang.org/library/std/traits/is_boolean.html

it has:


enum isBoolean(T) = is(BooleanTypeOf!T) && !isAggregateType!T;

per:
https://dlang.org/library/std/traits/is_aggregate_type.html

isAggregateType is true for [struct, union, class, interface].

So BooleanTypeOf!T is true for structs, unions, classes and 
interfaces? And if yes, why is that so?

Mike Parker <aldacron gmail.com> writes:

On Sunday, 18 February 2018 at 14:52:37 UTC, Tony wrote:
 At
 https://dlang.org/library/std/traits/is_boolean.html

 it has:


 enum isBoolean(T) = is(BooleanTypeOf!T) && !isAggregateType!T;

 per:
 https://dlang.org/library/std/traits/is_aggregate_type.html

 isAggregateType is true for [struct, union, class, interface].

 So BooleanTypeOf!T is true for structs, unions, classes and 
 interfaces? And if yes, why is that so?

Generally, no. But with alias this, it can be:

=====
import std.traits : BooleanTypeOf;
import std.stdio : writeln;

struct NoBool {
     int x;
}

struct AliasThisBool {
     bool b;
     alias b this;
}

void main()
{
     static if(is(BooleanTypeOf!NoBool)) writeln("NoBool");
     static if(is(BooleanTypeOf!AliasThisBool)) 
writeln("AliasThisBool");
}
=====

Tony <tonytdominguez aol.com> writes:

On Sunday, 18 February 2018 at 15:12:50 UTC, Mike Parker wrote:

 Generally, no. But with alias this, it can be:

 =====
 import std.traits : BooleanTypeOf;
 import std.stdio : writeln;

 struct NoBool {
     int x;
 }

 struct AliasThisBool {
     bool b;
     alias b this;
 }

 void main()
 {
     static if(is(BooleanTypeOf!NoBool)) writeln("NoBool");
     static if(is(BooleanTypeOf!AliasThisBool)) 
 writeln("AliasThisBool");
 }

Thanks!

It doesn't appear that BooleanTypeof is documented on dlang.org 
(outside of it's placement on the isBooleanType page). At least 
it isn't coming up in a "BooleanTypeOf site:dlang.org" search and 
not on the traits page:

https://dlang.org/library/std/traits.html

Basile B. <b2.temp gmx.com> writes:

On Monday, 19 February 2018 at 13:07:08 UTC, Tony wrote:
 It doesn't appear that BooleanTypeof is documented on dlang.org 
 (outside of it's placement on the isBooleanType page). At least 
 it isn't coming up in a "BooleanTypeOf site:dlang.org" search 
 and not on the traits page:

 https://dlang.org/library/std/traits.html

Indeed but Phobos maintainers don't want the ...TypeOf family to 
be documented.
(https://github.com/dlang/phobos/pull/5747)

Tony <tonytdominguez aol.com> writes:

On Monday, 19 February 2018 at 13:47:15 UTC, Basile B. wrote:

 Indeed but Phobos maintainers don't want the ...TypeOf family 
 to be documented.
 (https://github.com/dlang/phobos/pull/5747)

Ok, thanks.

But, assuming there is a use case for it, what if you want to 
restrict to a type that is either boolean, or a struct/class that 
can substitute for boolean - how do you do that without using the 
"private" TypeOfBoolean thing?

Nathan S. <no.public.email example.com> writes:

On Monday, 19 February 2018 at 15:12:15 UTC, Tony wrote:
 But, assuming there is a use case for it, what if you want to 
 restrict to a type that is either boolean, or a struct/class 
 that can substitute for boolean - how do you do that without 
 using the "private" TypeOfBoolean thing?


In that case you can just write `is(T : bool)`.

Tony <tonytdominguez aol.com> writes:

On Monday, 19 February 2018 at 17:22:04 UTC, Nathan S. wrote:
 On Monday, 19 February 2018 at 15:12:15 UTC, Tony wrote:
 But, assuming there is a use case for it, what if you want to 
 restrict to a type that is either boolean, or a struct/class 
 that can substitute for boolean - how do you do that without 
 using the "private" BooleanTypeOf thing?


 In that case you can just write `is(T : bool)`.

Thanks.

Assuming it would substitute, that should probably be used on 
this page in place of BooleanTypeOf since BooleanTypeOf is not 
supposed to be public:

https://dlang.org/library/std/traits/is_boolean.html

"enum isBoolean(T) = is(BooleanTypeOf!T) && !isAggregateType!T;"