Re: How do I set a class member value by its name in a string?
Always helpful. Thank you very much guys.
Re: How do I set a class member value by its name in a string?
On Wednesday, 27 December 2017 at 23:47:14 UTC, Biotronic wrote: [...] much, much better. thanks biotronic.
Re: How do I set a class member value by its name in a string?
On Wednesday, 27 December 2017 at 21:42:53 UTC, Mengu wrote:
On Wednesday, 27 December 2017 at 21:39:49 UTC, Mengu wrote:
On Wednesday, 27 December 2017 at 20:54:17 UTC, bitwise wrote:
[...]
there's also a simple workaround for fields with the same
type: https://run.dlang.io/is/dsFajq
import std.stdio;
struct S {
int x;
int y;
}
auto setValue(ref S s, string field, int value) {
foreach (fieldName; __traits(allMembers, S)) {
if (fieldName == field) {
__traits(getMember, s, fieldName) = value;
break;
}
}
}
void main() {
S s;
s.setValue("x", 5);
s.setValue("y", 25);
writeln(s);
}
you can play with it to make it more generic. you can also
create a mixin template that would generate setters for each
field you would need a setter for and then in the run time
you'd just be able to call them.
return type should just be void. that's just my muscle memory.
:-D
More generic, for more better:
void setValue(T, V)(auto ref T aggregate, string field, V value)
{
import std.traits : FieldNameTuple;
import std.meta : Alias;
switch (field)
{
foreach (fieldName; FieldNameTuple!T)
{
case fieldName:
static if (is(typeof(__traits(getMember,
aggregate, fieldName) = value)))
{
__traits(getMember, aggregate, fieldName) =
value;
return;
}
else assert(false, T.stringof ~ "."~field~"
cannot be assigned from a "~V.stringof~".");
}
default:
assert(false, T.stringof ~ " has no field named
"~field~".");
}
}
unittest {
import std.exception : assertThrown;
import core.exception : AssertError;
static struct S {
int x;
string s;
}
S s;
s.setValue("x", 14);
assert(s.x == 14);
assertThrown!AssertError(s.setValue("q", 14));
assertThrown!AssertError(s.setValue("s", 14));
s.setValue("s", "abc123");
assert(s.s == "abc123");
}
unittest {
import std.exception : assertThrown;
import core.exception : AssertError;
static class C {
int x;
string s;
}
C c = new C;
c.setValue("x", 14);
assert(c.x == 14);
assertThrown!AssertError(c.setValue("q", 14));
assertThrown!AssertError(c.setValue("s", 14));
c.setValue("s", "abc123");
assert(c.s == "abc123");
(new C).setValue("x", 143);
}
--
Biotronic
Re: How do I set a class member value by its name in a string?
On Wednesday, 27 December 2017 at 21:39:49 UTC, Mengu wrote:
On Wednesday, 27 December 2017 at 20:54:17 UTC, bitwise wrote:
[...]
there's also a simple workaround for fields with the same type:
https://run.dlang.io/is/dsFajq
import std.stdio;
struct S {
int x;
int y;
}
auto setValue(ref S s, string field, int value) {
foreach (fieldName; __traits(allMembers, S)) {
if (fieldName == field) {
__traits(getMember, s, fieldName) = value;
break;
}
}
}
void main() {
S s;
s.setValue("x", 5);
s.setValue("y", 25);
writeln(s);
}
you can play with it to make it more generic. you can also
create a mixin template that would generate setters for each
field you would need a setter for and then in the run time
you'd just be able to call them.
return type should just be void. that's just my muscle memory. :-D
Re: How do I set a class member value by its name in a string?
On Wednesday, 27 December 2017 at 20:54:17 UTC, bitwise wrote:
On Wednesday, 27 December 2017 at 20:04:29 UTC, Marc wrote:
I'd like to set the members of a class by its name at runtime,
I would do something like this:
__traits(getMember, myClass, name) = value;
but since name is only know at runtime, I can't use
__traits(). What's a workaround for this?
I think you could write something using a combination of these
two things:
https://dlang.org/phobos/std_traits.html#FieldNameTuple
https://dlang.org/phobos/std_traits.html#Fields
or maybe '.tupleof':
https://dlang.org/spec/struct.html#struct_properties
there's also a simple workaround for fields with the same type:
https://run.dlang.io/is/dsFajq
import std.stdio;
struct S {
int x;
int y;
}
auto setValue(ref S s, string field, int value) {
foreach (fieldName; __traits(allMembers, S)) {
if (fieldName == field) {
__traits(getMember, s, fieldName) = value;
break;
}
}
}
void main() {
S s;
s.setValue("x", 5);
s.setValue("y", 25);
writeln(s);
}
you can play with it to make it more generic. you can also create
a mixin template that would generate setters for each field you
would need a setter for and then in the run time you'd just be
able to call them.
Re: How do I set a class member value by its name in a string?
On Wednesday, 27 December 2017 at 20:04:29 UTC, Marc wrote: I'd like to set the members of a class by its name at runtime, I would do something like this: __traits(getMember, myClass, name) = value; but since name is only know at runtime, I can't use __traits(). What's a workaround for this? I think you could write something using a combination of these two things: https://dlang.org/phobos/std_traits.html#FieldNameTuple https://dlang.org/phobos/std_traits.html#Fields or maybe '.tupleof': https://dlang.org/spec/struct.html#struct_properties
Re: How do I set a class member value by its name in a string?
On Wednesday, 27 December 2017 at 20:04:29 UTC, Marc wrote:
I'd like to set the members of a class by its name at runtime,
I would do something like this:
__traits(getMember, myClass, name) = value;
but since name is only know at runtime, I can't use __traits().
What's a workaround for this?
You will have to use a combination of compile time and runtime
methologies.
Essentially what you want is this:
void setMemberValue(string name, int value)
{
switch(name)
{
case "member1":
member1 = value;
break;
case "member2":
member2 = value;
break:
...
}
}
As you don't want to write this for all members by hand you
should write a function which generates the source code for this
switch using static foreach and __traits(allMembers) and then
mixin the generated string into the setMemberValue method. If
your members can have different types you will also need runtime
type that can hold multiple types. For simplicity I just used
"int" in the above example. You could use "std.variant" for this.
How do I set a class member value by its name in a string?
I'd like to set the members of a class by its name at runtime, I would do something like this: __traits(getMember, myClass, name) = value; but since name is only know at runtime, I can't use __traits(). What's a workaround for this?
