On Mon, 16 Nov 2009 23:36:38 +0300, Derek Parnell <[email protected]> wrote:
On Mon, 16 Nov 2009 14:34:37 +0100, Don wrote:
bearophile wrote:
Don:
(providing that empty fall-through case statements remain valid;
disallowing them would be really annoying).
What's bad about forcing people to write:
case A, B, C:
Instead of:
case A:
case B:
case C:
?
Bye,
bearophile
(1) "case A, B, C:" implies a relationship between A, B, and C, which
might not exist. They may have nothing in common.
(2) it's an extremely common coding style in C, C++.
(3) it's more difficult to read.
(1) case A:
case B:
case C:
implies that there is no relationship between A,B, and C, but which
might actually exist. They may have something common.
(2) it's an extremely common writing style in human languages, thus aids
readability.
(3) case A:
case B:
case C:
is ambiguous. It looks like the coder put in place markers for
intended
code but forgot the code.
When porting some C++ code to D (okay, it was DMDFE), I had exact same
issue. There is the following macro defined:
#define CASE_BASIC_TYPES \
case TOKwchar: case TOKdchar: \
case TOKbit: case TOKbool: case TOKchar: \
case TOKint8: case TOKuns8: \
case TOKint16: case TOKuns16: \
case TOKint32: case TOKuns32: \
case TOKint64: case TOKuns64: \
case TOKfloat32: case TOKfloat64: case TOKfloat80: \
case TOKimaginary32: case TOKimaginary64: case TOKimaginary80: \
case TOKcomplex32: case TOKcomplex64: case TOKcomplex80: \
case TOKvoid
and if was used (and got translated to D) as follows:
switch (token) {
case TOKidentifier:
case TOKenum:
case TOKstruct:
case TOKimport:
CASE_BASIC_TYPES:
}
Did you noticed it already? It is a valid C code *but* has different
semantics! In D, CASE_BASIC_TYPES is merely a label, and it does just
nothing. Needless to say the code compiled successfully, but produced
weird error messages at run-time.
BTW, if a macro was declared as
#define BASIC_TYPES \
TOKwchar: case TOKdchar: \
case TOKbit: case TOKbool: case TOKchar: \
case TOKint8: case TOKuns8: \
case TOKint16: case TOKuns16: \
case TOKint32: case TOKuns32: \
case TOKint64: case TOKuns64: \
case TOKfloat32: case TOKfloat64: case TOKfloat80: \
case TOKimaginary32: case TOKimaginary64: case TOKimaginary80: \
case TOKcomplex32: case TOKcomplex64: case TOKcomplex80: \
case TOKvoid
(note an absence of the first case) then it would cause compile-time error
instead of run-time bugs. Usage:
switch (token) {
case TOKidentifier:
case TOKenum:
case TOKstruct:
case TOKimport:
case BASIC_TYPES:
}
