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digitalmars.D.learn - How use "toHash" without cast

reply "Namespace" <rswhite4 googlemail.com> writes:
hello, iI have written a template vector class. Now I need to 
rewrite the tohash function in dependence to the coords. But i 
have no clue because it doesn't allow any casts or convertions, 
because its a  trusted method.
Because of that i cannot override toHash for float, real or 
double.
Any ideas?
Jun 20 2012
parent reply =?UTF-8?B?QWxleCBSw7hubmUgUGV0ZXJzZW4=?= <alex lycus.org> writes:
On 21-06-2012 00:31, Namespace wrote:

 hello, iI have written a template vector class. Now I need to rewrite
 the tohash function in dependence to the coords. But i have no clue
 because it doesn't allow any casts or convertions, because its a
  trusted method.
 Because of that i cannot override toHash for float, real or double.
 Any ideas?


I don't really understand the problem. I think you need to show some code.

 trusted doesn't actually affect whether you can cast or convert anything.

-- 
Alex Rønne Petersen
alex lycus.org
http://lycus.org
Jun 20 2012
parent reply "Namespace" <rswhite4 googlemail.com> writes:
That is my Code:

[code]
class Vector2D(T) {
private:
	static Vector2D!(T) CastFromObject(Object o) {
		import std.typetuple;

		foreach (Type; TypeTuple!(byte, ubyte, short, ushort, int, 
uint, long, ulong, float, double, real)) {
			if (auto vec = cast(Vector2D!(Type)) o) {
				return cast(Vector2D!(T)) vec;
			}
		}

		return null;
	}
	
public:
	T x;
	T y;
	
	this(T x, T y) {
		this.x = x;
		this.y = y;
	}
	
	static Vector2D!(T) opCall(T x, T y) {
		return new Vector2D!(T)(x, y);
	}
	
	float Summe() const pure nothrow {
		return this.x + this.y;
	}
	
	override bool opEquals(Object o) const {
		if (o is null) {
			debug {
				writeln("Object is null ;)");
			}

			return false;
		}

		const Vector2D!(T) vec = CastFromObject(o);

		if (vec is this) {
			return true;
		}

		return (vec.x == this.x) && (vec.y == this.y);
	}
	
	override hash_t toHash() const pure nothrow {
		return this.x + this.y;
	}
	
	override int opCmp(Object o) const {
		if (o is null) {
			return -1;
		}

		const Vector2D vec = CastFromObject(o);

		if (vec is this) {
			return 0;
		}

		if (this.Summe() > vec.Summe()) {
			return 1;
		}

		if (this.Summe() < vec.Summe()) {
			return -1;
		}

		return 0;
	}
	
	override string toString() const {
		return "Vector2D!(" ~ T.stringof ~ ")(" ~ to!(string)(this.x) ~ 
", " ~ to!(string)(this.y) ~ ")";
	}
}

[/code]

I have dmd 2.059 and with my current version of toHash i get the 
compiler errors, that he cannot implicit convert from float, 
real, double, long and so on to uint.
I cannot solve the problem with a simple cast or to!uint because 
then he said that casts form float to uint are not allowed or 
that to! isn't trusted and nothrow. I hate such annoying errors...
Jun 20 2012
parent reply "Jonathan M Davis" <jmdavisProg gmx.com> writes:
On Thursday, June 21, 2012 00:43:49 Namespace wrote:

 That is my Code:
 
 [code]
 class Vector2D(T) {
 private:
 static Vector2D!(T) CastFromObject(Object o) {
 import std.typetuple;
 
 foreach (Type; TypeTuple!(byte, ubyte, short, ushort, int,
 uint, long, ulong, float, double, real)) {
 if (auto vec = cast(Vector2D!(Type)) o) {
 return cast(Vector2D!(T)) vec;
 }
 }
 
 return null;
 }
 
 public:
 T x;
 T y;
 
 this(T x, T y) {
 this.x = x;
 this.y = y;
 }
 
 static Vector2D!(T) opCall(T x, T y) {
 return new Vector2D!(T)(x, y);
 }
 
 float Summe() const pure nothrow {
 return this.x + this.y;
 }
 
 override bool opEquals(Object o) const {
 if (o is null) {
 debug {
 writeln("Object is null ;)");
 }
 
 return false;
 }
 
 const Vector2D!(T) vec = CastFromObject(o);
 
 if (vec is this) {
 return true;
 }
 
 return (vec.x == this.x) && (vec.y == this.y);
 }
 
 override hash_t toHash() const pure nothrow {
 return this.x + this.y;
 }
 
 override int opCmp(Object o) const {
 if (o is null) {
 return -1;
 }
 
 const Vector2D vec = CastFromObject(o);
 
 if (vec is this) {
 return 0;
 }
 
 if (this.Summe() > vec.Summe()) {
 return 1;
 }
 
 if (this.Summe() < vec.Summe()) {
 return -1;
 }
 
 return 0;
 }
 
 override string toString() const {
 return "Vector2D!(" ~ T.stringof ~ ")(" ~ to!(string)(this.x) ~
 ", " ~ to!(string)(this.y) ~ ")";
 }
 }
 
 [/code]
 
 I have dmd 2.059 and with my current version of toHash i get the
 compiler errors, that he cannot implicit convert from float,
 real, double, long and so on to uint.
 I cannot solve the problem with a simple cast or to!uint because
 then he said that casts form float to uint are not allowed or
 that to! isn't trusted and nothrow. I hate such annoying errors...


Eventually, toHash will have to be  safe const pure nothrow, but I don't think 
that the compiler requires that yet (though work was being done on that, so it 
may). You didn't mark toHash as  safe though, so it may be inferring it from 
Object (I believe that it _has_ been changed so that attributes are now 
inferred from the base class declarations when overriding). So, toHash may be 
being inferred as  safe. Try marking toHash as  trusted. If that doesn't work, 
then move its implementation into another function which you mark as  trusted 
and have toHash call it (since  safe can call  trusted but can't do  system 
stuff, unlike  trusted).

- Jonathan M Davis
Jun 20 2012
parent reply =?UTF-8?B?QWxleCBSw7hubmUgUGV0ZXJzZW4=?= <alex lycus.org> writes:
On 21-06-2012 03:13, Jonathan M Davis wrote:

 On Thursday, June 21, 2012 00:43:49 Namespace wrote:

 That is my Code:

 [code]
 class Vector2D(T) {
 private:
 static Vector2D!(T) CastFromObject(Object o) {
 import std.typetuple;

 foreach (Type; TypeTuple!(byte, ubyte, short, ushort, int,
 uint, long, ulong, float, double, real)) {
 if (auto vec = cast(Vector2D!(Type)) o) {
 return cast(Vector2D!(T)) vec;
 }
 }

 return null;
 }

 public:
 T x;
 T y;

 this(T x, T y) {
 this.x = x;
 this.y = y;
 }

 static Vector2D!(T) opCall(T x, T y) {
 return new Vector2D!(T)(x, y);
 }

 float Summe() const pure nothrow {
 return this.x + this.y;
 }

 override bool opEquals(Object o) const {
 if (o is null) {
 debug {
 writeln("Object is null ;)");
 }

 return false;
 }

 const Vector2D!(T) vec = CastFromObject(o);

 if (vec is this) {
 return true;
 }

 return (vec.x == this.x)&&  (vec.y == this.y);
 }

 override hash_t toHash() const pure nothrow {
 return this.x + this.y;
 }

 override int opCmp(Object o) const {
 if (o is null) {
 return -1;
 }

 const Vector2D vec = CastFromObject(o);

 if (vec is this) {
 return 0;
 }

 if (this.Summe()>  vec.Summe()) {
 return 1;
 }

 if (this.Summe()<  vec.Summe()) {
 return -1;
 }

 return 0;
 }

 override string toString() const {
 return "Vector2D!(" ~ T.stringof ~ ")(" ~ to!(string)(this.x) ~
 ", " ~ to!(string)(this.y) ~ ")";
 }
 }

 [/code]

 I have dmd 2.059 and with my current version of toHash i get the
 compiler errors, that he cannot implicit convert from float,
 real, double, long and so on to uint.
 I cannot solve the problem with a simple cast or to!uint because
 then he said that casts form float to uint are not allowed or
 that to! isn't trusted and nothrow. I hate such annoying errors...


 Eventually, toHash will have to be  safe const pure nothrow, but I don't think
 that the compiler requires that yet (though work was being done on that, so it
 may). You didn't mark toHash as  safe though, so it may be inferring it from
 Object (I believe that it _has_ been changed so that attributes are now
 inferred from the base class declarations when overriding). So, toHash may be
 being inferred as  safe. Try marking toHash as  trusted. If that doesn't work,
 then move its implementation into another function which you mark as  trusted
 and have toHash call it (since  safe can call  trusted but can't do  system
 stuff, unlike  trusted).

 - Jonathan M Davis


It's actually  trusted as per the docs. I do not know why DMD infers 
that to be  safe.....

In any case, the solution here is this:

     override hash_t toHash()  trusted const pure nothrow {
         return cast(hash_t)(this.x + this.y);
     }

-- 
Alex Rønne Petersen
alex lycus.org
http://lycus.org
Jun 20 2012
next sibling parent =?UTF-8?B?QWxleCBSw7hubmUgUGV0ZXJzZW4=?= <alex lycus.org> writes:
On 21-06-2012 04:30, Alex Rønne Petersen wrote:

 On 21-06-2012 03:13, Jonathan M Davis wrote:

 On Thursday, June 21, 2012 00:43:49 Namespace wrote:

 That is my Code:

 [code]
 class Vector2D(T) {
 private:
 static Vector2D!(T) CastFromObject(Object o) {
 import std.typetuple;

 foreach (Type; TypeTuple!(byte, ubyte, short, ushort, int,
 uint, long, ulong, float, double, real)) {
 if (auto vec = cast(Vector2D!(Type)) o) {
 return cast(Vector2D!(T)) vec;
 }
 }

 return null;
 }

 public:
 T x;
 T y;

 this(T x, T y) {
 this.x = x;
 this.y = y;
 }

 static Vector2D!(T) opCall(T x, T y) {
 return new Vector2D!(T)(x, y);
 }

 float Summe() const pure nothrow {
 return this.x + this.y;
 }

 override bool opEquals(Object o) const {
 if (o is null) {
 debug {
 writeln("Object is null ;)");
 }

 return false;
 }

 const Vector2D!(T) vec = CastFromObject(o);

 if (vec is this) {
 return true;
 }

 return (vec.x == this.x)&& (vec.y == this.y);
 }

 override hash_t toHash() const pure nothrow {
 return this.x + this.y;
 }

 override int opCmp(Object o) const {
 if (o is null) {
 return -1;
 }

 const Vector2D vec = CastFromObject(o);

 if (vec is this) {
 return 0;
 }

 if (this.Summe()> vec.Summe()) {
 return 1;
 }

 if (this.Summe()< vec.Summe()) {
 return -1;
 }

 return 0;
 }

 override string toString() const {
 return "Vector2D!(" ~ T.stringof ~ ")(" ~ to!(string)(this.x) ~
 ", " ~ to!(string)(this.y) ~ ")";
 }
 }

 [/code]

 I have dmd 2.059 and with my current version of toHash i get the
 compiler errors, that he cannot implicit convert from float,
 real, double, long and so on to uint.
 I cannot solve the problem with a simple cast or to!uint because
 then he said that casts form float to uint are not allowed or
 that to! isn't trusted and nothrow. I hate such annoying errors...


 Eventually, toHash will have to be  safe const pure nothrow, but I
 don't think
 that the compiler requires that yet (though work was being done on
 that, so it
 may). You didn't mark toHash as  safe though, so it may be inferring
 it from
 Object (I believe that it _has_ been changed so that attributes are now
 inferred from the base class declarations when overriding). So, toHash
 may be
 being inferred as  safe. Try marking toHash as  trusted. If that
 doesn't work,
 then move its implementation into another function which you mark as
  trusted
 and have toHash call it (since  safe can call  trusted but can't do
  system
 stuff, unlike  trusted).

 - Jonathan M Davis


 It's actually  trusted as per the docs. I do not know why DMD infers
 that to be  safe.....

 In any case, the solution here is this:

 override hash_t toHash()  trusted const pure nothrow {
 return cast(hash_t)(this.x + this.y);
 }


Filed a bug: http://d.puremagic.com/issues/show_bug.cgi?id=8275

-- 
Alex Rønne Petersen
alex lycus.org
http://lycus.org
Jun 20 2012
prev sibling parent reply "Namespace" <rswhite4 googlemail.com> writes:
 It's actually  trusted as per the docs. I do not know why DMD 
 infers that to be  safe.....

 In any case, the solution here is this:

     override hash_t toHash()  trusted const pure nothrow {
         return cast(hash_t)(this.x + this.y);
     }


Yes, it's already trusted.

If I write " trusted const pure nothrow" it works fine, but if i 
write "const pure nothrow" not. Why? I thought the compiler is 
orientating at the base method which is overriden.
Jun 21 2012
parent reply Jonathan M Davis <jmdavisProg gmx.com> writes:
On Thursday, June 21, 2012 09:48:52 Namespace wrote:

 It's actually  trusted as per the docs. I do not know why DMD
 infers that to be  safe.....
 
 In any case, the solution here is this:
     override hash_t toHash()  trusted const pure nothrow {
     
         return cast(hash_t)(this.x + this.y);
     
     }


 
 Yes, it's already trusted.
 
 If I write " trusted const pure nothrow" it works fine, but if i
 write "const pure nothrow" not. Why? I thought the compiler is
 orientating at the base method which is overriden.


Apparently, when you override an  trusted method, the method in the derived 
class is inferred to be  safe - which makes sense when you think about it, 
since the derived class' function hasn't done anything  system. If it calls 
the base class' version, which is  trusted, then it can be  safe. So, as long 
as it doesn't do anything  system itself, it can be  safe. However, since the 
compiler doesn't infer any attributes from the derived class' function's body 
(since it's not templated), if you do any  system stuff in there, it'll give 
you a compilation error rather than treating it as  system - though that makes 
sense too, since having a derived class function with worse guarantees than a 
base class function isn't valid. So, even if the attributes _were_ inferred 
from the function's body, it would _still_ have to give you an error, since 
the body would be  system when it needed to be at least  trusted.

http://d.puremagic.com/issues/show_bug.cgi?id=8275

- Jonathan M Davis
Jun 21 2012
parent "Namespace" <rswhite4 googlemail.com> writes:
I see, a bit confusing but I think I understand.
Thank you. :)
Jun 21 2012