Author: Jan Nijtmans <[email protected]> State: Draft Type: Project Vote: In progress Post-History: Keywords: Tcl Tcl_GetBoolFromObj() Tcl_GetBool() Tcl-Version: 8.7 Tcl-Branch: tip-618
This TIP proposes new functions
Tcl_GetBool which are the same as
Tcl_GetBoolean but have an additional
flags parameter, and use
as variable type. Also accepted is the
TCL_NULL_OK flag, which is - actually - a renamed
TCL_INDEX_NULL_OK: We wouldn't want a separate
Tcl_GetBoolean is provided the
TCL_NULL_OK flag, it can
output not only 0 or 1 but also '\xFF'. Without the
TCL_NULL_OK flag, the only
possible outcomes are 0 and 1. In Tcl, there is not much usage for the
flag but in Tk it is more common to have values which can be empty as well as 0 or 1.
underline options of text tags.
Tcl_GetBoolean store a boolean value
int, which - in many cases - is overkill since 0 and 1 are the
only possible value.
With the new functions, we can do:
#include <tcl.h> char bool1; Tcl_Obj *obj = Tcl_NewStringObj("true", -1); Tcl_GetBoolFromObj(NULL, obj, 0, &bool1);
Also, the functions
Tcl_GetBool have an additional
flags parameter. At this moment only the values 0 and
are allowed. Thanks to the
TCL_NULL_OK flag, we can replace
code in Tk with a single call to
-underline options for text tags are already mentioned,
that's the intended usage of this flag.
Other flag values can be added in the future.
This TIP has been in vote before, with the result of only gaining one YES vote and 3 PRESENT votes. There were 2 main remarks, indicating this TIP did too many things at once, the implications of that couldn't be grasped by the voters. Therefore, the TIP has been rewritten (and the implementation simplified). The remarks were:
- "... I don't think I grok the entire implications of the discussion we had on this list about (void *) abuses".
In C, "void *" can be used when the function accepts multiple different types.
memcpy() are perfect examples, but also the use of
ClientData in Tcl is not an abuse of "void *". The caller is responsible
making sure that a pointer of the correct type is used. In the case of
Tcl_GetBool, the function accepts any 1-, 2-, 4-
or 8-byte enum, bool or integer type. As long as the functions know
the sizeof() of the variable, no invalid memory will be addressed.
The suggestion is also done to split this into different functions depending on the sizeof() the variable. That would be possible, but then 8 new functions should be added, and - still - a "void *" should be used as last argument: possible 1-byte types could be bool, char, signed char or unsigned char. 2-byte types could be VARIANT_BOOL, wchar_t, short or unsigned short. We don't want functions for every possible type here, when the sizeof() the variable is the only thing we really care about.
- "Even after sleeping over it I find myself unable to agree to the macro shenanigans for the transmission of the size of the referenced variable, even while admiring the hackishness of it."
The implementation rewrite doesn't use macro's any more.
Available in the
This branch targets 8.7.
This document has been placed in the public domain.