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```{index} single: Params::Util
```

# Params::Util

```{pperl-module-badges} Params::Util
```

Check parameters: each function returns its argument if it is a value
of the kind the name says, and `undef` if not.

`_STRING` is a defined, non-empty, non-reference value; `_NUMBER` one
that is or looks like a number. `_SCALAR`, `_ARRAY`, `_HASH` and
`_CODE` are unblessed references to such a thing, the plain names
non-empty, the `0` forms (`_SCALAR0`, `_ARRAY0`, `_HASH0`) empty too.
`_ARRAYLIKE`, `_HASHLIKE` and `_CODELIKE` also accept objects that
overload `@{}`, `%{}` or `&{}`. `_REGEX` is a compiled regex,
`_INSTANCE($obj, $class)` an object that `isa` `$class`.

These are the compiled functions of Params::Util 1.102; its
`Params/Util.pm` and `Params/Util/PP.pm` are used unchanged, and the
functions it has no compiled form of (`_IDENTIFIER`, `_CLASS`,
`_POSINT`, `_SET`, `_HANDLE`, ...) come from `Params::Util::PP`.


## Synopsis

```perl
use Params::Util qw(_STRING _HASH _INSTANCE);

sub new {
    my $class = shift;
    my $name  = _STRING(shift)         or die "no name";
    my $opts  = _HASH(shift) // {};
    my $log   = _INSTANCE(shift, 'Log') or die "no logger";
    ...
}
```

## Differences from upstream

None.

## Modules

- [`Params::Util::PP`](Util/PP.md) - PurePerl Params::Util routines

## Functions

### Value checks

#### `_STRING`

The value itself if it is a defined, non-reference string of at least one character (a number counts, in its string form), else `undef`.

**Synopsis**

```perl
my $name = _STRING($in) or die "need a name";
```

#### `_NUMBER`

The value itself if it is a number, or a non-empty string that looks like one (`looks_like_number`), else `undef`.

**Synopsis**

```perl
my $n = _NUMBER($in) // die "not a number";
```

### Reference checks

#### `_SCALAR0`

An unblessed reference to a scalar, whatever it holds, else `undef`.

#### `_SCALAR`

An unblessed reference to a scalar holding a non-empty string, else `undef`.

**Synopsis**

```perl
my $text = _SCALAR($ref) or die "need a reference to some text";
```

#### `_REGEX`

A compiled regex (`qr//`), else `undef`.

#### `_ARRAY0`

An unblessed array reference, empty or not, else `undef`.

#### `_ARRAY`

An array reference with at least one element, else `undef`.

**Synopsis**

```perl
my $list = _ARRAY($in) or die "need a non-empty list";
```

#### `_ARRAYLIKE`

An array reference, or an object that overloads `@{}`, else `undef`.

#### `_HASH0`

A hash reference, empty or not, else `undef`.

#### `_HASH`

A hash reference with at least one key, else `undef`.

**Synopsis**

```perl
my $opts = _HASH($in) || {};
```

#### `_HASHLIKE`

A hash reference, or an object that overloads `%{}`, else `undef`.

#### `_CODE`

A code reference, else `undef`.

#### `_CODELIKE`

A code reference, or an object that overloads `&{}`, else `undef`.

#### `_INSTANCE`

An object that `isa` the class given (its own `isa` method decides), else `undef`; an empty class name is never matched.

**Synopsis**

```perl
my $dbh = _INSTANCE($in, 'DBI::db') or die "need a database handle";
```

```{toctree}
:hidden:
:maxdepth: 1

Util/PP
```