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[subsection {Custom Types, Semi-trivial}]
A more involved custom argument type would be to map from Tcl strings
to some internal representation, like an integer code.
[para] The first example is taken from the [package tclyaml] package,
a binding to the [package libyaml] library. In a few places we have to
map readable names for block styles, scalar styles, etc. to the
internal enumeration.
[example {
critcl::argtype yaml_sequence_style_t {
if (!encode_sequence_style (interp, @@, &@A)) return TCL_ERROR;
}
...
critcl::ccode {
static const char* ty_block_style_names [] = {
"any", "block", "flow", NULL
};
static int
encode_sequence_style (Tcl_Interp* interp, Tcl_Obj* style,
yaml_sequence_style_t* estyle)
{
int value;
if (Tcl_GetIndexFromObj (interp, style, ty_block_style_names,
"sequence style", 0, &value) != TCL_OK) {
return 0;
}
*estyle = value;
return 1;
}
}
...
method sequence_start proc {
pstring anchor
pstring tag
int implicit
yaml_sequence_style_t style
} ok {
/* Syntax: <instance> seq_start <anchor> <tag> <implicit> <style> */
...
}
...
}]
It should be noted that this code precedes the advent of the
supporting generator package [package critcl::emap]. using the
generator the definition of the mapping becomes much simpler:
[example {
critcl::emap::def yaml_sequence_style_t {
any 0
block 1
flow 2
}
}]
Note that the generator will not only provide the conversions, but
also define the argument and result types needed for their use by
[cmd critcl::cproc].
Another example of such a semi-trivial argument type can be found in
the [package CRIMP] package, which defines a [type Tcl_ObjType] for
[term image] values. This not only provides a basic argument type for
any image, but also derived types which check that the image has a
specific format. Here we see for the first time non-integer arguments,
and the need to define the C types used for variables holding the C
level value, and the type of function parameters (Due to C promotion
rules we may need different types).
[example {
critcl::argtype image {
if (crimp_get_image_from_obj (interp, @@, &@A) != TCL_OK) {
return TCL_ERROR;
}
} crimp_image* crimp_image*
...
set map [list <<type>> $type]
critcl::argtype image_$type [string map $map {
if (crimp_get_image_from_obj (interp, @@, &@A) != TCL_OK) {
return TCL_ERROR;
}
if (@A->itype != crimp_imagetype_find ("crimp::image::<<type>>")) {
Tcl_SetObjResult (interp,
Tcl_NewStringObj ("expected image type <<type>>",
-1));
return TCL_ERROR;
}
}] crimp_image* crimp_image*
...
}]
|
