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digitalmars.D.learn - Defining inout returned values for ranges

reply Jonathan Crapuchettes <jcrapuchettes gmail.com> writes:
If a range struct (Range) is defined inside another struct (Test), how 
can the constness or mutability of Test be attributed to the return type 
of Range.front? I'm running into this problem because I need the range to 
be iterated, but I need the pointer in T to be marked const when 
appropriate.

Thank you,
JC

Pseudo-Example:
struct Test
{
    static struct T
    {
        uint* ptr;
    }
    ...

    auto opSlice() inout
    {
        static struct Range
        {
            inout(T) front()  property
            {
                ...
            }
            ...
        }

        return Range();
    }
}
Sep 03 2013
parent reply "anonymous" <anonymous example.com> writes:
On Wednesday, 4 September 2013 at 00:56:39 UTC, Jonathan 
Crapuchettes wrote:

 If a range struct (Range) is defined inside another struct 
 (Test), how
 can the constness or mutability of Test be attributed to the 
 return type
 of Range.front? I'm running into this problem because I need 
 the range to
 be iterated, but I need the pointer in T to be marked const when
 appropriate.

 Thank you,
 JC

 Pseudo-Example:
 struct Test
 {
     static struct T
     {
         uint* ptr;
     }
     ...

     auto opSlice() inout
     {
         static struct Range
         {
             inout(T) front()  property
             {
                 ...
             }
             ...
         }

         return Range();
     }
 }



You can use a Template This Parameter [1] instead of inout:
----
    auto opSlice(this This)()
    {
        static if(is(This == const)) alias QualifiedT = const T;
        else alias QualifiedT = T;

        static struct Range
        {
            QualifiedT front()  property
            {
----

[1] http://dlang.org/template.html#TemplateThisParameter
Sep 04 2013
parent reply Jonathan Crapuchettes <jcrapuchettes gmail.com> writes:
On Wed, 04 Sep 2013 11:49:41 +0200, anonymous wrote:


 On Wednesday, 4 September 2013 at 00:56:39 UTC, Jonathan Crapuchettes
 wrote:

 If a range struct (Range) is defined inside another struct (Test), how
 can the constness or mutability of Test be attributed to the return
 type of Range.front? I'm running into this problem because I need the
 range to be iterated, but I need the pointer in T to be marked const
 when appropriate.

 Thank you,
 JC

 Pseudo-Example:
 struct Test {
     static struct T {
         uint* ptr;
     }
     ...

     auto opSlice() inout {
         static struct Range {
             inout(T) front()  property {
                 ...
             }
             ...
         }

         return Range();
     }
 }


 
 
 You can use a Template This Parameter [1] instead of inout:
 ----
     auto opSlice(this This)()
     {
         static if(is(This == const)) alias QualifiedT = const T;
         else alias QualifiedT = T;
 
         static struct Range {
             QualifiedT front()  property {
 ----
 
 [1] http://dlang.org/template.html#TemplateThisParameter


Thank you for the help. That worked, but now I ran into another similar 
issue. What if the Range struct is being defined outside of the opSlice 
method? I have a number of methods in a struct that return the same range 
type and would rather not have to have duplicate code or need to use 
mixins.

JC
Sep 05 2013
parent reply "anonymous" <anonymous example.com> writes:
On Thursday, 5 September 2013 at 19:19:42 UTC, Jonathan 
Crapuchettes wrote:

 On Wed, 04 Sep 2013 11:49:41 +0200, anonymous wrote:


[...]

 You can use a Template This Parameter [1] instead of inout:
 ----
     auto opSlice(this This)()
     {
         static if(is(This == const)) alias QualifiedT = const 
 T;
         else alias QualifiedT = T;
 
         static struct Range {
             QualifiedT front()  property {
 ----
 
 [1] http://dlang.org/template.html#TemplateThisParameter


 Thank you for the help. That worked, but now I ran into another 
 similar
 issue. What if the Range struct is being defined outside of the 
 opSlice
 method? I have a number of methods in a struct that return the 
 same range
 type and would rather not have to have duplicate code or need 
 to use
 mixins.

 JC


Templatize Range and pass it This:
----
    static struct Range(This)
    {
        static if(is(This == const)) alias QualifiedT = const T;
        else alias QualifiedT = T;

        QualifiedT front()  property {...}
    }

    auto opSlice(this This)()
    {
        return Range!This();
    }

    ... more methods in the style of opSlice ...
----

If you need QualifiedT in opSlice, make it a template over This, 
too.
Sep 05 2013
parent Jonathan Crapuchettes <jcrapuchettes gmail.com> writes:
On Thu, 05 Sep 2013 23:32:10 +0200, anonymous wrote:


 On Thursday, 5 September 2013 at 19:19:42 UTC, Jonathan Crapuchettes
 wrote:

 On Wed, 04 Sep 2013 11:49:41 +0200, anonymous wrote:


 [...]

 You can use a Template This Parameter [1] instead of inout:
 ----
     auto opSlice(this This)()
     {
         static if(is(This == const)) alias QualifiedT = const
 T;
         else alias QualifiedT = T;
 
         static struct Range {
             QualifiedT front()  property {
 ----
 
 [1] http://dlang.org/template.html#TemplateThisParameter


 Thank you for the help. That worked, but now I ran into another similar
 issue. What if the Range struct is being defined outside of the opSlice
 method? I have a number of methods in a struct that return the same
 range type and would rather not have to have duplicate code or need to
 use mixins.

 JC


 
 Templatize Range and pass it This:
 ----
     static struct Range(This)
     {
         static if(is(This == const)) alias QualifiedT = const T;
         else alias QualifiedT = T;
 
         QualifiedT front()  property {...}
     }
 
     auto opSlice(this This)()
     {
         return Range!This();
     }
 
     ... more methods in the style of opSlice ...
 ----
 
 If you need QualifiedT in opSlice, make it a template over This,
 too.


Thank you again. It all appears to be working correctly.

JC
Sep 06 2013