NAME

    Data::Checks - Value constraint checking

SYNOPSIS

    With Signature::Attribute::Checked:

       use v5.26;
       use Sublike::Extended;
       use Signature::Attribute::Checked;
    
       use Data::Checks qw( Str );
    
       extended sub greet ( $message :Checked(Str) ) {
          say "Hello, $message";
       }
    
       greet( "world" );  # is fine
       greet( undef );    # throws an exception

    With Object::Pad::FieldAttr::Checked:

       use v5.22;
       use Object::Pad;
       use Object::Pad::FieldAttr::Checked;
    
       use Data::Checks qw( Str );
    
       class Datum {
          field $name :param :reader :Checked(Str);
       }
    
       my $x = Datum->new( name => "something" );  # is fine
       my $y = Datum->new( name => undef );        # throws an exception

DESCRIPTION

    This module provides functions that implement various value constraint
    checking behaviours. These are the parts made visible by the use
    Data::Checks ... import line, in Perl code.

    It also provides the underlying common framework XS functions to assist
    in writing modules that actually implement such constraint checking.
    These parts are not visible in Perl code, but instead made visible at
    the XS level by the #include "DataChecks.h" directive.

CONSTRAINTS

    The following constraint checks are inspired by the same-named ones in
    Types::Standard. They may be called fully-qualified, or imported
    lexically into the calling scope.

    Note to users familiar with Types::Standard: some of these functions
    behave slightly differently. In particular, these constraints are
    generally happy to accept an object reference to a class that provides
    a conversion overload, whereas the ones in Types::Standard often are
    not.

 Defined

       Defined()

    Passes for any defined value, fails only for undef.

 Object

       Object()

    Passes for any blessed object reference, fails for non-references or
    references to unblessed data.

 Str

       Str()

    Passes for any defined non-reference value, or a reference to an object
    in a class that overloads stringification. Fails for undefined,
    unblessed references, or references to objects in classes that do not
    overload stringification.

 Num

       Num()

    Passes for any defined non-reference value that is either a plain
    number, or a string that could be used as one without warning, or a
    reference to an object in a class that overloads numification. Fails
    for undefined, strings that would raise a warning if converted to a
    number, unblessed references, or references to objects in classes that
    do not overload numification.

XS FUNCTIONS

    The following functions are provided by the DataChecks.h header file
    for use in XS modules that implement value constraint checking.

 boot_data_checks

       void boot_data_checks(double ver);

    Call this function from your BOOT section in order to initialise the
    module and load the rest of the support functions.

    ver should either be 0 or a decimal number for the module version
    requirement; e.g.

       boot_data_checks(0.01);

 make_checkdata

       struct DataChecks_Checker *make_checkdata(SV *checkspec);

    Creates a struct DataChecks_Checker structure, which wraps the intent
    of the value constraint check. The returned value is used as the
    checker argument for the remaining functions.

    The constraint check itself is specified by the SV given by checkspec,
    which should come directly from the user code. The constraint check may
    be specified in any of three ways:

      * An object reference in a class which has a check method. Value
      checks will be invoked as

         $ok = $checkerobj->check( $value );

      * A package name as a plain string of a package which has a check
      method. Value checks will be invoked as

         $ok = $checkerpkg->check( $value );

      * A code reference. Value checks will be invoked with a single
      argument, as

         $ok = $checkersub->( $value );

      * Additionally, the constraint check functions provided by this
      module may be implemented using any of the above mechanisms, or may
      use an unspecified fourth different mechanism. Outside code should
      not rely on what that mechanism may be.

    Once constructed into a checker structure, the choice of which
    implementation is used is fixed, and if a method lookup is involved its
    result is stored directly as a CV pointer for efficiency of later
    invocations. In either of the first two cases, the reference count on
    the checkspec SV is increased to account for the argument value used on
    each invocation. In the third case, the reference SV is not retained,
    but the underlying CV it refers to has its reference count increased.

 free_checkdata

       void free_checkdata(struct DataChecks_Checker *checker);

    Releases any stored SVs in the checker structure, and the structure
    itself.

 gen_assertmess

       void gen_assertmess(struct DataChecks_Checker *checker, SV *name, SV *constraint);

    Generates and stores a message string for the assert message to be used
    by "make_assertop" and "assert_value". The message will take the form

       NAME requires a value satisfying CONSTRAINT

    Both name and constraint SVs used as temporary strings to generate the
    stored message string. Neither SV is retained by the checker directly.

 make_assertop

       OP *make_assertop(struct DataChecks_Checker *checker, OP *argop);

    Creates an optree fragment for a value check assertion operation.

    Given an optree fragment in scalar context that generates an argument
    value (argop), constructs a larger optree fragment that consumes it and
    checks that the value passes the constraint check given by checker. The
    returned optree fragment will operate in void context (i.e. it does not
    yield the argument value itself).

 check_value

       bool check_value(struct DataChecks_Checker *checker, SV *value);

    Checks whether a given SV passes the given constraint check, returning
    true if so, or false if not.

 assert_value

       void assert_value(struct DataChecks_Checker *checker, SV *value);

    Checks whether a given SV passes the given constraint check, throwing
    its assertion message if it does not.

AUTHOR

    Paul Evans <leonerd@leonerd.org.uk>