** Synopsis **

    :   '''`[namespace] qualifiers`''' ''string''



** Description **

'''`namespace qualifiers`''' is the complement (almost - see below) of `[namespace tail]`.
It returns the leading namespace qualifiers for ''string'', or, when ''string'' is `::`, the [empty string].
Qualifiers are namespace names separated by `::`.
The operation of `namespace qualifiers` is purely lexical.  It does not check whether the namespace names exist.



** Examples **

The value of

======
namespace qualifiers ::foo::bar::x
======

is

======none
::foo::bar
======

** Issues **

Namespace qualifiers is inconsistent when applied to names in the root namespace:
======
% namespace qualifiers ::foo::bar
::foo
% namespace qualifiers foo::bar
foo
% namespace qualifiers foo

% namespace qualifiers ::foo

======

This makes it a bit tricky to use correctly.  Using [ensemble extend] it's not hard to write a more ergonomic version:
======
extend namespace {
    proc join {prefix name} {
        if {[string match ::* $name]} {
            return $name
        }
        if {$prefix eq "::"} {
            return ::$name
        }
        return ${prefix}::$name
    }
    proc prefix {name} {
        string range $name 0 end-[string length [namespace tail $name]]
    }
}
======

With these two procs, `$x` is always equal to:
======
namespace join [
    namespace prefix $x
] [
    namespace tail $x
]
======

** See Also **

   [namespace]:   

<<categories>> Command | Tcl syntax help