https://issues.dlang.org/show_bug.cgi?id=12732
Issue ID: 12732
Summary: Add an Appender-like template that recursively builds
a structure of Appender fields
Product: D
Version: D2
Hardware: All
OS: All
Status: NEW
Severity: enhancement
Priority: P1
Component: Phobos
Assignee: nob...@puremagic.com
Reporter: andrej.mitrov...@gmail.com
This seems to be a common occurrence in my code:
-----
import std.array;
alias vec3 = int[3];
///
struct Model
{
vec3[] indices;
vec3[] vertices;
vec3[] normals;
}
Model loadModel(string path)
{
// note the code duplication here, needs to be tracked
// separately to the Model struct.
Appender!(vec3[]) indices;
Appender!(vec3[]) vertices;
Appender!(vec3[]) normals;
// ...
// indices ~=
// vertices ~=
return Model(indices.data, vertices.data, normals.data);
}
void main() { }
-----
To avoid this code duplication it would be great to have a helper template that
can return an equivalent structure which contains Appender fields for all
internal arrays, and a convenience .data property function that returns the
original type. Here's one implementation:
-----
import std.array;
import std.typetuple;
alias vec3 = int[3];
alias ApplyAppender(T : E[], E) = Appender!T;
alias ApplyAppender(T) = T;
struct AppenderWrapper(T)
{
alias Fields = staticMap!(ApplyAppender, typeof(T.tupleof));
Fields fields;
alias fields this;
@property T data()
{
T res;
foreach (idx, field; fields)
{
static if (is(typeof(res.tupleof[idx]) : E[], E))
res.tupleof[idx] = field.data;
else
res.tupleof[idx] = field;
}
return res;
}
}
///
struct Model
{
vec3[] indices;
vec3[] vertices;
vec3[] normals;
}
Model loadModel(string path)
{
AppenderWrapper!(typeof(return)) result;
// ...
// result.indices ~=
// result.vertices ~=
return result.data;
}
void main() { }
-----
--
