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.\" ========================================================================
.\"
.IX Title "Class::MethodMaker::hash 3pm"
.TH Class::MethodMaker::hash 3pm "2020-11-08" "perl v5.32.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Class::Method::hash \- Create methods for handling a hash value.
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&  use Class::MethodMaker
\&    [ hash => [qw/ x /] ];
\&
\&  $instance\->x;                 # empty
\&  $instance\->x(a => 1, b => 2, c => 3);
\&  $instance\->x_count == 3;      # true
\&  $instance\->x = (b => 5, d => 8); # Note this *replaces* the hash,
\&                                   # not adds to it
\&  $instance\->x_index(\*(Aqb\*(Aq) == 5; # true
\&  $instance\->x_exists(\*(Aqc\*(Aq);     # false
\&  $instance\->x_exists(\*(Aqd\*(Aq);     # true
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Creates methods to handle hash values in an object.  For a component named
\&\f(CW\*(C`x\*(C'\fR, by default creates methods \f(CW\*(C`x\*(C'\fR, \f(CW\*(C`x_reset\*(C'\fR, \f(CW\*(C`x_clear\*(C'\fR, \f(CW\*(C`x_isset\*(C'\fR,
\&\f(CW\*(C`x_count\*(C'\fR, \f(CW\*(C`x_index\*(C'\fR, \f(CW\*(C`x_keys\*(C'\fR, \f(CW\*(C`x_values\*(C'\fR, \f(CW\*(C`x_each\*(C'\fR, \f(CW\*(C`x_exists\*(C'\fR,
\&\f(CW\*(C`x_delete\*(C'\fR, \f(CW\*(C`x_set\*(C'\fR, \f(CW\*(C`x_get\*(C'\fR.
.PP
Methods available are:
.PP
\fI\f(CI\*(C`*\*(C'\fI\fR
.IX Subsection "*"
.PP
\&\fICreated by default\fR.  This method returns the list of keys and values stored
in the slot (they are returned pairwise, i.e., key, value, key, value; as with
perl hashes, no order of keys is guaranteed).  If any arguments are provided
to this method, they \fBreplace\fR the current hash contents.  In an array
context it returns the keys, values as an array and in a scalar context as a
hash-reference.  Note that this reference is no longer a direct reference to
the storage, in contrast to Class::MethodMaker v1.  This is to protect
encapsulation.  See x_ref if you need that functionality (and are prepared to
take the associated risk.)
.PP
If a single argument is provided that is an arrayref or hashref, it is
expanded and its contents used in place of the existing contents.  This is a
more efficient passing mechanism for large numbers of values.
.PP
\fI\f(CI*_reset\fI\fR
.IX Subsection "*_reset"
.PP
\&\fICreated by default\fR.  Called without an argument, this resets the component
as a whole; deleting any associated storage, and returning the component to
its default state.  Normally, this means that \fI*_isset\fR will return false,
and \fI*\fR will return undef.  If \f(CW\*(C`\-default\*(C'\fR is in effect, then the component
will be set to the default value, and \fI*_isset\fR will return true.  If
\&\f(CW\*(C`\-default_ctor\*(C'\fR is in effect, then the default subr will be invoked, and its
return value used to set the value of the component, and \fI*_isset\fR will
return true.
.PP
If called with arguments, these arguments are treated as indexes into the
component, and the individual elements thus referenced are reset (their
storage deleted, so that \fI*_isset(n)\fR will return false for appropriate \fIn\fR,
except where \f(CW\*(C`\-default\*(C'\fR or \f(CW\*(C`\-default_ctor\*(C'\fR are in force, as above).  As with
perl arrays, resetting the highest set value implicitly decreases the count
(but x_reset(n) never unsets the aggregate itself, even if all the elements
are not set).
.PP
\fI\f(CI*_clear\fI\fR
.IX Subsection "*_clear"
.PP
\&\fICreated by default\fR.  Empty the component of all elements, but without
deleting the storage itself.
.PP
If given a list of keys, then the elements \fIthat exist\fR indexed by those keys
are set to undef (but not deleted).
.PP
Note the very different semantics: \f(CW\*(C`$x\->a_clear(\*(Aqb\*(Aq)\*(C'\fR sets the value of
\&\f(CW\*(C`b\*(C'\fR in component 'a' to undef (if \f(CW\*(C`b\*(C'\fR) already exists (so \f(CW\*(C`$x\->a_isset(\*(Aqb\*(Aq))\*(C'\fR returns true), but \f(CW\*(C`$x\->a_clear()\*(C'\fR deletes the
element \f(CW\*(C`b\*(C'\fR from component 'a' (so \f(CW\*(C`$x\->a_isset(\*(Aqb\*(Aq))\*(C'\fR returns false).
.PP
\fI\f(CI*_isset\fI\fR
.IX Subsection "*_isset"
.PP
\&\fICreated by default\fR.  Whether the component is currently set.  This is
different from being defined; initially, the component is not set (and if
read, will return undef); it can be set to undef (which is a set value, which
also returns undef).  Having been set, the only way to unset the component is
with \f(CW*_reset\fR.
.PP
If a default value is in effect, then \f(CW*_isset\fR will always return true.
.PP
\&\fI*\f(BI_isset()\fI\fR tests the component as a whole.  \fI*_isset(a)\fR tests the element
indexed by \fIa\fR.  \fI*_isset(a,b)\fR tests the elements indexed by \fIa\fR, \fIb\fR,
and returns the logical conjunction (\fIand\fR) of the tests.
.PP
\fI\f(CI*_count\fI\fR
.IX Subsection "*_count"
.PP
\&\fICreated by default\fR.  Returns the number of elements in this component.
This is not affected by presence (or lack) of a \f(CW\*(C`default\*(C'\fR (or
\&\f(CW\*(C`default_ctor\*(C'\fR).  Returns \f(CW\*(C`undef\*(C'\fR if whole component not set (as per
\&\fI*_isset\fR).
.PP
\fI\f(CI*_index\fI\fR
.IX Subsection "*_index"
.PP
\&\fICreated by default\fR.  Takes a list of indices, returns a list of the
corresponding values.
.PP
If a default (or a default ctor) is in force, then a lookup by
index will vivify & set to the default the respective elements (and
therefore the aggregate data-structure also, if it's not already).
.PP
\fI\f(CI*_keys\fI\fR
.IX Subsection "*_keys"
.PP
\&\fICreated by default\fR.  The known keys, as a list in list context, as an
arrayref in scalar context.
.PP
If you're expecting a count of the keys in scalar context, see \fI*_count\fR.
.PP
\fI\f(CI*_values\fI\fR
.IX Subsection "*_values"
.PP
\&\fICreated by default\fR.  The known values, as a list in list context, as an
arrayref in scalar context.
.PP
\fI\f(CI*_each\fI\fR
.IX Subsection "*_each"
.PP
\&\fICreated by default\fR.  The next pair of key, value (as a list) from the hash.
.PP
\fI\f(CI*_exists\fI\fR
.IX Subsection "*_exists"
.PP
\&\fICreated by default\fR.  Takes any number of arguments, considers each as a
key, and determines whether the key exists in the has.  Returns the logical
conjunction (\fIand\fR).
.PP
\fI\f(CI*_delete\fI\fR
.IX Subsection "*_delete"
.PP
\&\fICreated by default\fR.  This operates exactly like \fI*_reset\fR, except that
calling this with no args does nothing.  This is provided for orthogonality
with the Perl \f(CW\*(C`delete\*(C'\fR operator, while \fI*_reset\fR is provided for
orthogonality with other component types.
.PP
\fI\f(CI*_set\fI\fR
.IX Subsection "*_set"
.PP
.Vb 3
\&  %n = $x\->h; # (a=>1,b=>2,c=>3) (in some order)
\&  $h\->h_set(b=>4,d=>7);
\&  %n = $h\->a; # (a=>1,b=>4,c=>3,d=>7) (in some order)
.Ve
.PP
\&\fICreated by default\fR.  Takes a list, treated as pairs of index => value; each
given index is set to the corresponding value.  No return.
.PP
If two arguments are given, of which the first is an arrayref, then it is
treated as a list of indices of which the second argument (which must also be
an arrayref) are the corresponding values.  Thus the following two commands
are equivalent:
.PP
.Vb 2
\&  $x\->a_set(b=>4,d=>7);
\&  $x\->a_set([\*(Aqb\*(Aq,\*(Aqd\*(Aq],[4,7]);
.Ve
.PP
\fI\f(CI*_get\fI\fR
.IX Subsection "*_get"
.PP
\&\fICreated by default\fR.  Retrieves the value of the component without setting
(ignores any arguments passed).