Re: Problem with immutables and Template typeof(this)
On 12/28/2014 02:07 PM, AuoroP via Digitalmars-d-learn wrote:
I have been trying to figure templates out...
Although the question has already been answered, here is a solution that
combines most of the suggestions that have already been made. It does
not need any kind of casting:
/* Eponymous template syntax is lighter */
struct ExampleTemplate(T)
{
T value;
this(T value)
{
this.value = value;
}
/* 1) As a shorthand, the name of the template is the same
*thing as this specific instantiation of it. For
*example, if the template is instantiated with int,
*then ExampleTemplate alone means
*ExampleTemplate!int.
*
* 2) opAdd is marked 'const' so that it can work on
*mutable, const, and immutable objects.
*
* 3) The parameter is by-copy so that it can take rvalues as well.
*/
ExampleTemplate opAdd(const(ExampleTemplate) that) const
{
return ExampleTemplate(this.value + that.value);
/* Alternatively:
auto result = ExampleTemplate(this.value + that.value);
return result;
*/
}
}
void main()
{
/* New alias syntax makes more sense */
alias Example = ExampleTemplate!int;
immutable immutableEx = Example(1);
Example ex = Example(1);
Example ex2 = immutableEx + ex + immutableEx;
}
Ali
Problem with immutables and Template typeof(this)
I have been trying to figure templates out...
template ExampleTemplate(T)
{
struct ExampleTemplate
{
T value;
// constructor
auto this(T value)
{
this.value = value;
return this;
}
// opAdd
typeof(this) opAdd(typeof(this) that) // immutable
{
typeof(this) result;
result.value = this.value + that.value;
return result;
}
}
}
alias ExampleTemplate!int Example;
immutable immutableEx = Example(1);
Example ex = Example(1);
Example ex2 = immutableEx + ex;
I get this error with mutbale opAdd:
example.d(27): Error: mutable method
example.ExampleTemplate!int.ExampleTemplate.opAdd is not
callable using a immutable object
I get this error with immutable opAdd
---~---+---~---=---~---+---~---
example.d(18): Error: cannot modify immutable expression
result.value
example.d(27): Error: template instance
example.ExampleTemplate!int error instantiating
I get that typeof(this) is immutable ExampleTemplate!int.
I can't find any way to cast immutable away because
typeof(this) is the only way I know to get the type.
Any help would be greatly appreciated!
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Re: Problem with immutables and Template typeof(this)
On Sunday, 28 December 2014 at 22:07:31 UTC, AuoroP via
Digitalmars-d-learn wrote:
I have been trying to figure templates out...
template ExampleTemplate(T)
{
struct ExampleTemplate
{
T value;
// constructor
auto this(T value)
{
this.value = value;
return this;
}
Constructor should not have a return value.
// opAdd
typeof(this) opAdd(typeof(this) that) // immutable
{
typeof(this) result;
result.value = this.value + that.value;
return result;
}
}
}
alias ExampleTemplate!int Example;
immutable immutableEx = Example(1);
Example ex = Example(1);
Example ex2 = immutableEx + ex;
I get this error with mutbale opAdd:
example.d(27): Error: mutable method
example.ExampleTemplate!int.ExampleTemplate.opAdd is not
callable using a immutable object
This is because you can only call member functions that are
marked with immutable, if your instance is immutable.
pragma(msg, typeof(this)) will print the type of this at compile
time.
I get this error with immutable opAdd
---~---+---~---=---~---+---~---
example.d(18): Error: cannot modify immutable expression
result.value
example.d(27): Error: template instance
example.ExampleTemplate!int error instantiating
This is because typeof(this) is immutable.
I get that typeof(this) is immutable ExampleTemplate!int.
I can't find any way to cast immutable away because
typeof(this) is the only way I know to get the type.
Well, the type is ExampleTemplate. No reason not to write it
directly. If you cannot for whatever reason I currently do not
see: cast to Unqual!(typeof(this)).
See http://dlang.org/phobos/std_traits.html
Re: Problem with immutables and Template typeof(this)
On Sun, 28 Dec 2014 14:07:18 -0800
AuoroP via Digitalmars-d-learn digitalmars-d-learn@puremagic.com
wrote:
let me give you a riddle:
struct ExampleTemplate(T) {
T value;
auto opAdd (typeof(this) that) inout {
import std.traits : Unqual;
Unqual!(typeof(this)) result;
result.value = this.value+that.value;
return result;
}
}
alias ExampleTemplate!int Example;
void main () {
immutable immutableEx = Example(1);
Example ex = Example(1);
Example ex2 = immutableEx+ex;
}
i tend to give some explanations to my answers here, but i'm in a
strange mood today, so sorry, no explanations this time.
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Re: Problem with immutables and Template typeof(this)
On Sunday, 28 December 2014 at 22:07:31 UTC, AuoroP via
Digitalmars-d-learn wrote:
I have been trying to figure templates out...
template ExampleTemplate(T)
{
struct ExampleTemplate
{
T value;
// constructor
auto this(T value)
Constructors don't have return types.
{
this.value = value;
return this;
Constructors don't return.
}
// opAdd
typeof(this) opAdd(typeof(this) that) // immutable
{
typeof(this) result;
result.value = this.value + that.value;
return result;
}
}
}
alias ExampleTemplate!int Example;
immutable immutableEx = Example(1);
Example ex = Example(1);
Example ex2 = immutableEx + ex;
I get this error with mutbale opAdd:
example.d(27): Error: mutable method
example.ExampleTemplate!int.ExampleTemplate.opAdd is not
callable using a immutable object
I get this error with immutable opAdd
---~---+---~---=---~---+---~---
example.d(18): Error: cannot modify immutable expression
result.value
example.d(27): Error: template instance
example.ExampleTemplate!int error instantiating
I get that typeof(this) is immutable ExampleTemplate!int.
I can't find any way to cast immutable away because
typeof(this) is the only way I know to get the type.
The type is ExampleTemplate, so:
ExampleTemplate result;
But if you actually need to, you can use std.traits.Unqual to get
the unqualified version of a type:
import std.traits: Unqual;
Unqual!(typeof(this)) result;
Re: Problem with immutables and Template typeof(this)
-Original Message-
From: digitalmars-d-learn@puremagic.com
Sent: Sun, 28 Dec 2014 22:18:43 +
To: digitalmars-d-learn@puremagic.com
Subject: Re: Problem with immutables and Template typeof(this)
On Sunday, 28 December 2014 at 22:07:31 UTC, AuoroP via
Digitalmars-d-learn wrote:
I have been trying to figure templates out...
template ExampleTemplate(T)
{
struct ExampleTemplate
{
T value;
// constructor
auto this(T value)
{
this.value = value;
return this;
}
Constructor should not have a return value.
Thank you!
// opAdd
typeof(this) opAdd(typeof(this) that) // immutable
{
typeof(this) result;
result.value = this.value + that.value;
return result;
}
}
}
alias ExampleTemplate!int Example;
immutable immutableEx = Example(1);
Example ex = Example(1);
Example ex2 = immutableEx + ex;
I get this error with mutbale opAdd:
example.d(27): Error: mutable method
example.ExampleTemplate!int.ExampleTemplate.opAdd is not
callable using a immutable object
This is because you can only call member functions that are
marked with immutable, if your instance is immutable.
pragma(msg, typeof(this)) will print the type of this at compile
time.
Thank you, that is easier than my method:
// opDbg
typeof(this) opDbg() immutable
{
writeln( typeof(this).stringof );
return this;
}
I get this error with immutable opAdd
---~---+---~---=---~---+---~---
example.d(18): Error: cannot modify immutable expression
result.value
example.d(27): Error: template instance
example.ExampleTemplate!int error instantiating
This is because typeof(this) is immutable.
I get that typeof(this) is immutable ExampleTemplate!int.
I can't find any way to cast immutable away because
typeof(this) is the only way I know to get the type.
Well, the type is ExampleTemplate. No reason not to write it
directly. If you cannot for whatever reason I currently do not
see: cast to Unqual!(typeof(this)).
See http://dlang.org/phobos/std_traits.html
I tried this and it works!!! I just don't get why it works. It /is/ a type but
it seems a parameter short of being useful! I definitely wouldn't have tried it
on my own so I'm really thankful for that!
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Re: Problem with immutables and Template typeof(this)
-Original Message-
From: digitalmars-d-learn@puremagic.com
Sent: Sun, 28 Dec 2014 22:21:20 +
To: digitalmars-d-learn@puremagic.com
Subject: Re: Problem with immutables and Template typeof(this)
On Sunday, 28 December 2014 at 22:07:31 UTC, AuoroP via
Digitalmars-d-learn wrote:
I have been trying to figure templates out...
template ExampleTemplate(T)
{
struct ExampleTemplate
{
T value;
// constructor
auto this(T value)
I also wanted to thank you for your very helpful answer!
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