digitalmars.D.learn - Getting only the data members of a type
- =?UTF-8?B?QWxpIMOHZWhyZWxp?= (45/45) Mar 31 2012 How can I determine just the data members of a struct or class,
- Artur Skawina (13/23) Mar 31 2012 [...]
- =?UTF-8?B?QWxpIMOHZWhyZWxp?= (62/85) Mar 31 2012 excluding the member functions? isCallable() comes short as member
- Artur Skawina (12/53) Apr 01 2012
- Jacob Carlborg (4/10) Apr 01 2012 But it accepts "foreach (i, t; typeof(S.tupleof))".
- Artur Skawina (9/14) Apr 01 2012 It does - thank you.
- Artur Skawina (4/28) Apr 01 2012 That should have been:
- Jacob Carlborg (10/25) Apr 01 2012 Yeah, it's a bit strange. One could think that it would be possible to
- Ary Manzana (22/46) Apr 01 2012 This is what I don't like about D. It gives you a hammer and everyone
- Jacob Carlborg (4/25) Apr 01 2012 I agree.
How can I determine just the data members of a struct or class, excluding the member functions? isCallable() comes short as member variable that have opCall() defined are also callable: import std.stdio; import std.traits; struct M { void opCall() {} } struct S { int i; M m; void foo() {} } void main() { foreach (member; __traits(allMembers, S)) { if (isCallable!(mixin("S." ~ member))) { writefln("%5s is a member function", member); } else { writefln("%5s is a member variable", member); } } } The output shows that S.m is a function but it is not: i is a member variable m is a member function <-- unexpected foo is a member function Wait! I found a solution before sending this message. :P isIntegral() works: if (isIntegral!(typeof(mixin("S." ~ member)))) { Now the output is: i is a member function m is a member variable <-- good but dubious foo is a member variable The reason is, isIntegral() specifically mentions built in types: http://dlang.org/phobos/std_traits.html#isIntegral <quote> Detect whether T is a built-in integral type. Types bool, char, wchar, and dchar are not considered integral. </quote> Thank you, Ali
Mar 31 2012
On 03/31/12 21:09, Ali Çehreli wrote:How can I determine just the data members of a struct or class, excluding the member functions? isCallable() comes short as member variable that have opCall() defined are also callable:[...]Wait! I found a solution before sending this message. :P isIntegral() works: if (isIntegral!(typeof(mixin("S." ~ member)))) { Now the output is: i is a member function m is a member variable <-- good but dubious foo is a member variable[...] Don't forget about templates (appear as members too, but don't have a type). This will print all fields of struct/class S: enum s = cast(S*)null; foreach (i, m; s.tupleof) { enum name = S.tupleof[i].stringof[4..$]; alias typeof(m) type; writef("(%s) %s\n", type.stringof, name); } Real Programmers don't use std.traits. ;) artur
Mar 31 2012
On 03/31/2012 09:09 PM, Artur Skawina wrote:On 03/31/12 21:09, Ali Çehreli wrote:excluding the member functions? isCallable() comes short as member variable that have opCall() defined are also callable:How can I determine just the data members of a struct or class,[...]isIntegral() works:Wait! I found a solution before sending this message. :Ptype). I see. We can't even use isCallable or isIntegral with a template member. Assuming S has this member function template: void bar(T)() {} Then we get the following error: /usr/include/d/dmd/phobos/std/traits.d(3223): Error: (S).bar(T) has no value I don't know a way of saying "if a template".if (isIntegral!(typeof(mixin("S." ~ member)))) { Now the output is: i is a member function m is a member variable<-- good but dubious foo is a member variable[...] Don't forget about templates (appear as members too, but don't have aThis will print all fields of struct/class S: enum s = cast(S*)null; foreach (i, m; s.tupleof) { enum name = S.tupleof[i].stringof[4..$]; alias typeof(m) type; writef("(%s) %s\n", type.stringof, name); } Real Programmers don't use std.traits. ;) arturYour method works but needing to iterate on a struct variable by s.tupleof and having to use the struct type as S.tupleof in the loop body is strange. Looks like S.tupleof[i].stringof is the answer for what I was looking for: import std.stdio; import std.traits; struct M { int i; this(int i) { this.i = i; } void opCall() {} } struct S { int i; M m; void foo() {} void bar(T)() {} } void main() { enum s = S(42, M(7)); foreach (i, m; s.tupleof) { writefln("%s:", i); enum name = S.tupleof[i].stringof[4..$]; alias typeof(m) type; writefln(" S.tupleof[i]: %s", S.tupleof[i].stringof); writefln(" (type) name : (%s) %s", type.stringof, name); writefln(" m : %s", m); writefln(" m.stringof : %s", m.stringof); } } The output: 0: S.tupleof[i]: (S).i (type) name : (int) i m : 42 m.stringof : 42 1: S.tupleof[i]: (S).m (type) name : (M) m m : M(7) m.stringof : m Ali
Mar 31 2012
On 04/01/12 08:18, Ali Çehreli wrote:On 03/31/2012 09:09 PM, Artur Skawina wrote:eg: static if (!__traits(compiles, &__traits(getMember, obj, name))) or just static if (!is(typeof(member)))On 03/31/12 21:09, Ali Çehreli wrote:I see. We can't even use isCallable or isIntegral with a template member. Assuming S has this member function template: void bar(T)() {} Then we get the following error: /usr/include/d/dmd/phobos/std/traits.d(3223): Error: (S).bar(T) has no value I don't know a way of saying "if a template".How can I determine just the data members of a struct or class, excluding the member functions? isCallable() comes short as member variable that have opCall() defined are also callable:[...]Wait! I found a solution before sending this message. :P isIntegral() works: if (isIntegral!(typeof(mixin("S." ~ member)))) { Now the output is: i is a member function m is a member variable<-- good but dubious foo is a member variable[...] Don't forget about templates (appear as members too, but don't have a type).That's because the compiler won't accept "foreach (i, t; S.tupleof)" and "*.tupleof[i].stringof" is necessary to get the original name. This would have worked too: enum name = *s.tupleof[i].stringof[4..$]; but obfuscates the code more and looks like dereferencing a null pointer. arturThis will print all fields of struct/class S: enum s = cast(S*)null; foreach (i, m; s.tupleof) { enum name = S.tupleof[i].stringof[4..$]; alias typeof(m) type; writef("(%s) %s\n", type.stringof, name); } Real Programmers don't use std.traits. ;) arturYour method works but needing to iterate on a struct variable by s.tupleof and having to use the struct type as S.tupleof in the loop body is strange.
Apr 01 2012
On 2012-04-01 11:27, Artur Skawina wrote:That's because the compiler won't accept "foreach (i, t; S.tupleof)" and "*.tupleof[i].stringof" is necessary to get the original name. This would have worked too: enum name = *s.tupleof[i].stringof[4..$]; but obfuscates the code more and looks like dereferencing a null pointer. arturBut it accepts "foreach (i, t; typeof(S.tupleof))". -- /Jacob Carlborg
Apr 01 2012
On 04/01/12 14:10, Jacob Carlborg wrote:On 2012-04-01 11:27, Artur Skawina wrote:It does - thank you. This means that that ugly null-to-pointer cast from my example can go, and all that's needed is: foreach (i, type; typeof(S.tupleof)) { enum name = S.tupleof[i].stringof[4..$]; writef("(%s) %s\n", type.stringof, name); } arturThat's because the compiler won't accept "foreach (i, t; S.tupleof)" andBut it accepts "foreach (i, t; typeof(S.tupleof))".
Apr 01 2012
On 04/01/12 11:27, Artur Skawina wrote:On 04/01/12 08:18, Ali Çehreli wrote:That should have been: enum name = typeof(*s).tupleof[i].stringof[4..$]; arturOn 03/31/2012 09:09 PM, Artur Skawina wrote:That's because the compiler won't accept "foreach (i, t; S.tupleof)" and "*.tupleof[i].stringof" is necessary to get the original name. This would have worked too: enum name = *s.tupleof[i].stringof[4..$]; but obfuscates the code more and looks like dereferencing a null pointer.This will print all fields of struct/class S: enum s = cast(S*)null; foreach (i, m; s.tupleof) { enum name = S.tupleof[i].stringof[4..$]; alias typeof(m) type; writef("(%s) %s\n", type.stringof, name); } Real Programmers don't use std.traits. ;) arturYour method works but needing to iterate on a struct variable by s.tupleof and having to use the struct type as S.tupleof in the loop body is strange.
Apr 01 2012
On 2012-04-01 08:18, Ali Çehreli wrote:On 03/31/2012 09:09 PM, Artur Skawina wrote:> > enum s = cast(S*)null; > foreach (i, m; s.tupleof) { > enum name = S.tupleof[i].stringof[4..$]; > alias typeof(m) type; > writef("(%s) %s\n", type.stringof, name); > } > > Real Programmers don't use std.traits. ;) > > artur Your method works but needing to iterate on a struct variable by s.tupleof and having to use the struct type as S.tupleof in the loop body is strange.Yeah, it's a bit strange. One could think that it would be possible to use "m.stringof" but that just returns the type. Instead of using "s.tupleof" it's possible to use "typeof(S.tupleof)". Have a look at: https://github.com/jacob-carlborg/orange/blob/master/orange/util/Reflection.d#L212 It's possible to get the type of a field as well, based on the name: https://github.com/jacob-carlborg/orange/blob/master/orange/util/Reflection.d#L237 -- /Jacob Carlborg
Apr 01 2012
On 4/1/12 8:09 PM, Jacob Carlborg wrote:On 2012-04-01 08:18, Ali Çehreli wrote:This is what I don't like about D. It gives you a hammer and everyone tries to solve all problems with that single hammer. Then you get duplicated code for basic stuff, like getting the type of a field, in many projects. It's a waste of time for a developer to have to sit down and think how we can cheat the compiler or make it talk to give us something it already knows, but only having a hammer to do so. Either put that in the language, or in the core library. But don't make people waste time. I'd suggest sending pull request with methods that accomplish those annoyances. On the other hand, take a look at the implementation of std.traits. Is it really a win to implement functionLinkage in D? Right here: https://github.com/D-Programming-Language/phobos/blob/master/std/traits.d#L704 you are repeating the linkages with their names, when that information is already available to the compiler. What's the point in duplicating information? The compiler already knows it, and much better than D. It could be implemented in a much simpler way. Is it just the pride of saying "Look what I can do with my powerful compile time reflection capabilities (basically stringof in that module)?" I'm not angry, but I don't think things are taking the correct direction...On 03/31/2012 09:09 PM, Artur Skawina wrote:Yeah, it's a bit strange. One could think that it would be possible to use "m.stringof" but that just returns the type. Instead of using "s.tupleof" it's possible to use "typeof(S.tupleof)". Have a look at: https://github.com/jacob-carlborg/orange/blob/master/orange/util/Reflection.d#L212 It's possible to get the type of a field as well, based on the name: https://github.com/jacob-carlborg/orange/blob/master/orange/util/Reflection.d#L237enum s = cast(S*)null; foreach (i, m; s.tupleof) { enum name = S.tupleof[i].stringof[4..$]; alias typeof(m) type; writef("(%s) %s\n", type.stringof, name); } Real Programmers don't use std.traits. ;) arturYour method works but needing to iterate on a struct variable by s.tupleof and having to use the struct type as S.tupleof in the loop body is strange.
Apr 01 2012
On 2012-04-02 02:43, Ary Manzana wrote:This is what I don't like about D. It gives you a hammer and everyone tries to solve all problems with that single hammer. Then you get duplicated code for basic stuff, like getting the type of a field, in many projects. It's a waste of time for a developer to have to sit down and think how we can cheat the compiler or make it talk to give us something it already knows, but only having a hammer to do so. Either put that in the language, or in the core library. But don't make people waste time. I'd suggest sending pull request with methods that accomplish those annoyances. On the other hand, take a look at the implementation of std.traits. Is it really a win to implement functionLinkage in D? Right here: https://github.com/D-Programming-Language/phobos/blob/master/std/traits.d#L704 you are repeating the linkages with their names, when that information is already available to the compiler. What's the point in duplicating information? The compiler already knows it, and much better than D. It could be implemented in a much simpler way. Is it just the pride of saying "Look what I can do with my powerful compile time reflection capabilities (basically stringof in that module)?" I'm not angry, but I don't think things are taking the correct direction...I agree. -- /Jacob Carlborg
Apr 01 2012