digitalmars.D.learn - Problem with immutables and Template typeof(this)
- AuoroP via Digitalmars-d-learn (43/43) Dec 28 2014 I have been trying to figure templates out...
- Tobias Pankrath (12/50) Dec 28 2014 Constructor should not have a return value.
- Tobias Pankrath (5/9) Dec 28 2014 Also: Casting with no Type or CastQual removes any top level
- anonymous (10/48) Dec 28 2014 Constructors don't have return types.
- AuoroP via Digitalmars-d-learn (12/85) Dec 28 2014 Thank you, that is easier than my method:
- AuoroP via Digitalmars-d-learn (4/23) Dec 28 2014 I also wanted to thank you for your very helpful answer!
- =?UTF-8?B?QWxpIMOHZWhyZWxp?= (41/42) Dec 29 2014 Although the question has already been answered, here is a solution that...
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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Dec 28 2014
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 objectThis 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 instantiatingThis 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
Dec 28 2014
"Tobias Pankrath" <tobias pankrath.net> 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.htmlAlso: Casting with no Type or CastQual removes any top level const, immutable, shared or inout type modifiers from the type of the UnaryExpression. shared int x; assert(is(typeof(cast()x) == int));
Dec 28 2014
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;
Dec 28 2014
-----Original Message----- From: digitalmars-d-learn puremagic.com Sent: Sun, 28 Dec 2014 22:18:43 +0000 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:Thank you!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, that is easier than my method: // opDbg typeof(this) opDbg() immutable { writeln( typeof(this).stringof ); 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 objectThis 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 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! ____________________________________________________________ FREE 3D EARTH SCREENSAVER - Watch the Earth right on your desktop! Check it out at http://www.inbox.com/earthI 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 instantiatingThis 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
Dec 28 2014
-----Original Message----- From: digitalmars-d-learn puremagic.com Sent: Sun, 28 Dec 2014 22:21:20 +0000 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 also wanted to thank you for your very helpful answer! ____________________________________________________________ FREE 3D EARTH SCREENSAVER - Watch the Earth right on your desktop! Check it out at http://www.inbox.com/earthI have been trying to figure templates out... template ExampleTemplate(T) { struct ExampleTemplate { T value; // constructor auto this(T value)
Dec 28 2014
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
Dec 29 2014