=begin pod

=TITLE role Blob

=SUBTITLE Immutable buffer for binary data ('Binary Large OBject')

    role Blob[::T = uint8] does Positional[T] does Stringy { }

The C<Blob> role is an immutable interface to binary types, and offers a
list-like interface to lists of integers, typically unsigned integers.

=head1 Methods

=head2 method new

Defined as:

    method new(*@codes)

Creates a C<Blob> from a list of integers.

    my $blob = Blob.new([1, 2, 3]);

=head2 method Bool

Defined as:

    multi method Bool(Blob:D:)

Returns C<False> if and only if the buffer is empty.

    my $blob = Blob.new();
    say $blob.Bool; # OUTPUT: «False␤»
    $blob = Blob.new([1, 2, 3]);
    say $blob.Bool; # OUTPUT: «True␤»

=head2 method elems

Defined as:

    multi method elems(Blob:D: --> Int:D)

Returns the number of elements of the buffer.

    my $blob = Blob.new([1, 2, 3]);
    say $blob.elems; # OUTPUT: «3␤»

=head2 method bytes

Defined as:

    method bytes(Blob:D: --> Int:D)

Returns the number of bytes used by the elements in the buffer.

    say Blob.new([1, 2, 3]).bytes;      # OUTPUT: «3␤»
    say blob16.new([1, 2, 3]).bytes;    # OUTPUT: «6␤»
    say blob64.new([1, 2, 3]).bytes;    # OUTPUT: «24␤»

=head2 method decode

Defined as:

    multi method decode(Blob:D: Str:D $encoding = 'UTF-8' --> Str:D)

Applies an encoding to turn the blob into a L<Str|/type/Str>.

    my Blob $blob = "string".encode('utf-8');
    say $blob.decode('utf-8'); # OUTPUT: «string␤»

On malformed utf-8 C<.decode> will throw X::AdHoc. To handle sloppy utf-8 use
C<utf8-c8>.

=head2 method subbuf

Defined as:

    multi method subbuf(Int $from, Int $len = self.elems --> Blob:D)
    multi method subbuf(Range $range --> Blob:D)

Extracts a part of the invocant buffer, starting from the index with
elements C<$from>, and taking C<$len> elements (or less if the buffer is
shorter), and creates a new buffer as the result.

    say Blob.new(1..10).subbuf(2, 4);    # OUTPUT: «Blob:0x<03 04 05 06>␤»
    say Blob.new(1..10).subbuf(*-2);     # OUTPUT: «Blob:0x<09 0a>␤»
    say Blob.new(1..10).subbuf(*-5,2);   # OUTPUT: «Blob:0x<06 07>␤»

For convenience, also allows a C<Range> to be specified to indicate which
part of the invocant buffer you would like:

    say Blob.new(1..10).subbuf(2..5);    # OUTPUT: «Blob:0x<03 04 05 06>␤»

=head2 method unpack

This method is considered B<experimental>, in order to use it you will need to do:

    use experimental :pack;


Defined as:

    method unpack(Blob:D: $template --> List:D)

Extracts features from the blob according to the template string, and
returns them as a list.

The template string consists of zero or more units that begin with an ASCII
letter, and are optionally followed by a quantifier.  The quantifier can be
C<*> (which typically stands for "use up the rest of the Blob here"), or a
positive integer (without a C<+>).

Whitespace between template units is ignored.

Examples of valid templates include C<"A4 C n*"> and C<"A*">.

The following letters are recognized:

=begin table

    Letter  Meaning
    ======  =======
    A       Extract a string, where each element of the Blob maps to a codepoint
    a       Same as A
    C       Extract an element from the blob as an integer
    H       Extracts a hex string
    L       Extracts four elements and returns them as a single unsigned integer
    n       Extracts two elements and combines them in "network" (big-endian) byte order into a single integer
    N       Extracts four elements and combines them in "network" (big-endian) byte order into a single integer
    S       Extracts two elements and returns them as a single unsigned integer
    v       Same as S
    V       Same as L
    x       Drop an element from the blob (that is, ignore it)
    Z       Same as A

=end table

Example:

    use experimental :pack;
    say Blob.new(1..10).unpack("C*");
    # OUTPUT: «(1 2 3 4 5 6 7 8 9 10)␤»

=head2 sub pack

This subroutine is considered B<experimental>,  in order to use it you will need to do:

=begin code :skip-test
use experimental :pack;
    sub pack(Str $template, *@items --> Buf)
=end code

Packs the given items according to the template and returns a buffer
containing the packed bytes.

The template string consists of zero or more units that begin with an ASCII
letter, and are optionally followed by a quantifier.  For details, see
L<unpack|/routine/unpack>.

=end pod
