string is an ensemble of commands for manipulating strings.
Is this correct behavior?
% set str {} % string is true $str 1 % string is false $str 1 % string is integer $str 1 % string is alpha $str 1
Sadly, yes, that is correct. You'll have to use the -strict option to keep empty strings from passing all tests.
This is an unfortunate legacy from the origin of string is as a tool for entry validation, where it's important the empty string pass everything so that every input doesn't fail immediately.
The following subcommands check for the ByteArray object type internally based on their bytecode versions (as of 8.5.0):
The following subcommands force promotion to unicode strings:
MG: Since Tcl 8.5, an index in the string commands can include basic math;
string range $string $startChar+1 $endChar-1
is now equivalent to
string range $string [expr {$startChar + 1}] [expr {$endChar - 1}]
While the first may be clearer, though, it seems to be (potentially quite a lot) slower for me, running 8.5a6:
% set string "This is a test string" This is a test string % set startChar 3 3 % set endChar 12 12
% time {string range $string [expr {$startChar+1}] [expr {$endChar-1}]} 500000 2.55498 microseconds per iteration % time {string range $string $startChar+1 $endChar-1} 500000 5.092856 microseconds per iteration
Using expr there is quite drastically faster...