digitalmars.D - Is there a standard way to define to for user-defined types?
- Jonathan M Davis (23/23) Jun 19 2011 For instance, if I want to make it legal to pass a core.time.TickDuratio...
- Paul D. Anderson (8/39) Jun 19 2011 I'd also like to see a solution to this, primarily because std.conv.to i...
- Dmitry Olshansky (5/44) Jun 20 2011 I think option #3 could be great, and the name of that templated
- Steven Schveighoffer (6/33) Jun 20 2011 I vote for 3. However, it should not be called 'to', because you may wa...
For instance, if I want to make it legal to pass a core.time.TickDuration to to!(core.time.Duration) instead of casting it (which is actually why I've been think of this issue), what is the standard way to do that? Or isn't there one? I'm not aware of one. And if there isn't one, how should we do it? I can think of 3 possible ways: 1. Overload to in the module with the type being converted from. So, for instance, core.time would have an overload for to which takes a TickDuration and returns a Duration (either that or std.datetime if it didn't work to have that in druntime for some reason). I'm not sure if that'll cause problems with overload sets or not though. 2. Make it so that std.conv.to can do its thing based on opCast. If a type overloads opCast, then std.conv.to can use that opCast to do the conversion (but only if opCast is defined, not for just any cast which may or may not be valid). 3. Make it so that user-defined types have a semi-standard member function (e.g. to) which std.conv.to looks for and uses for conversions if it's there. Which of those would you consider to be the best? Or can you think of another, better way? It seems to me that we need an essentially standard way of defining conversions which use to. Otherwise, the only option is to use opCast, and while there's nothing wrong with overloading opCast, it would definitely be preferable to use to for safe conversions. Thoughts? - Jonathan M Davis
Jun 19 2011
Jonathan M Davis Wrote:For instance, if I want to make it legal to pass a core.time.TickDuration to to!(core.time.Duration) instead of casting it (which is actually why I've been think of this issue), what is the standard way to do that? Or isn't there one? I'm not aware of one. And if there isn't one, how should we do it? I can think of 3 possible ways: 1. Overload to in the module with the type being converted from. So, for instance, core.time would have an overload for to which takes a TickDuration and returns a Duration (either that or std.datetime if it didn't work to have that in druntime for some reason). I'm not sure if that'll cause problems with overload sets or not though. 2. Make it so that std.conv.to can do its thing based on opCast. If a type overloads opCast, then std.conv.to can use that opCast to do the conversion (but only if opCast is defined, not for just any cast which may or may not be valid). 3. Make it so that user-defined types have a semi-standard member function (e.g. to) which std.conv.to looks for and uses for conversions if it's there. Which of those would you consider to be the best? Or can you think of another, better way? It seems to me that we need an essentially standard way of defining conversions which use to. Otherwise, the only option is to use opCast, and while there's nothing wrong with overloading opCast, it would definitely be preferable to use to for safe conversions. Thoughts? - Jonathan M DavisI'd also like to see a solution to this, primarily because std.conv.to is so useful. overloading. But maybe I didn't do it right. Along this same line, is there a way to write a ToImpl that std.conv can recognize? Again, I've tried this without success, but that doesn't mean it can't be done. to. But it would be better than nothing. toString() function, which is great for to!string In my case, I've created an alternative conversion module and only implemented the types I need; then I've added the types I defined. But I know this will bite me when I try to integrate with other modules. I don't care much how this is implemented but it would be a very useful tool. Paul
Jun 19 2011
On 20.06.2011 7:56, Paul D. Anderson wrote:Jonathan M Davis Wrote:function could be ... to! -- Dmitry OlshanskyFor instance, if I want to make it legal to pass a core.time.TickDuration to to!(core.time.Duration) instead of casting it (which is actually why I've been think of this issue), what is the standard way to do that? Or isn't there one? I'm not aware of one. And if there isn't one, how should we do it? I can think of 3 possible ways: 1. Overload to in the module with the type being converted from. So, for instance, core.time would have an overload for to which takes a TickDuration and returns a Duration (either that or std.datetime if it didn't work to have that in druntime for some reason). I'm not sure if that'll cause problems with overload sets or not though. 2. Make it so that std.conv.to can do its thing based on opCast. If a type overloads opCast, then std.conv.to can use that opCast to do the conversion (but only if opCast is defined, not for just any cast which may or may not be valid). 3. Make it so that user-defined types have a semi-standard member function (e.g. to) which std.conv.to looks for and uses for conversions if it's there. Which of those would you consider to be the best? Or can you think of another, better way? It seems to me that we need an essentially standard way of defining conversions which use to. Otherwise, the only option is to use opCast, and while there's nothing wrong with overloading opCast, it would definitely be preferable to use to for safe conversions. Thoughts? - Jonathan M DavisI'd also like to see a solution to this, primarily because std.conv.to is so useful. overloading. But maybe I didn't do it right. Along this same line, is there a way to write a ToImpl that std.conv can recognize? Again, I've tried this without success, but that doesn't mean it can't be done. to. But it would be better than nothing. toString() function, which is great for to!string In my case, I've created an alternative conversion module and only implemented the types I need; then I've added the types I defined. But I know this will bite me when I try to integrate with other modules. I don't care much how this is implemented but it would be a very useful tool. Paul
Jun 20 2011
On Sun, 19 Jun 2011 23:22:23 -0400, Jonathan M Davis <jmdavisProg gmx.com> wrote:For instance, if I want to make it legal to pass a core.time.TickDuration to to!(core.time.Duration) instead of casting it (which is actually why I've been think of this issue), what is the standard way to do that? Or isn't there one? I'm not aware of one. And if there isn't one, how should we do it? I can think of 3 possible ways: 1. Overload to in the module with the type being converted from. So, for instance, core.time would have an overload for to which takes a TickDuration and returns a Duration (either that or std.datetime if it didn't work to have that in druntime for some reason). I'm not sure if that'll cause problems with overload sets or not though. 2. Make it so that std.conv.to can do its thing based on opCast. If a type overloads opCast, then std.conv.to can use that opCast to do the conversion (but only if opCast is defined, not for just any cast which may or may not be valid). 3. Make it so that user-defined types have a semi-standard member function (e.g. to) which std.conv.to looks for and uses for conversions if it's there.I vote for 3. However, it should not be called 'to', because you may want to call to!X(y) in a member function, which would resolve to your member to, not the global to. -Steve
Jun 20 2011