NAME
String::BufferStack - Nested buffers for templating systems
SYNOPSIS
my $stack = String::BufferStack->new;
$stack->push( filter => sub {return uc shift} );
$stack->append("content");
$stack->flush_output;
DESCRIPTION
"String::BufferStack" provides a framework for storing nested buffers.
By default, all of the buffers flow directly to the output method, but
individual levels of the stack can apply filters, or store their output
in a scalar reference.
METHODS
new PARAMHASH
Creates a new buffer stack and returns it. Possible arguments include:
prealoc
Preallocate this many bytes in the output buffer. This can reduce
reallocations, and thus speed up appends.
out_method
The method to call when output trickles down to the bottom-most
buffer and is flushed via flush_output. The default "out_method"
prints the content to "STDOUT". This method will always be called
with non-undef, non-zero length content.
push PARAMHASH
Pushes a new frame onto the buffer stack. By default, the output from
this new frame connects to the input of the previous frame. There are a
number of possible options:
buffer
A string reference, into which the output from this stack frame will
appear. By default, this is the input buffer of the previous frame.
private
If a true value is passed for "private", it creates a private string
reference, and uses that as the buffer -- this is purely for
convenience. That is, the following blocks are equivilent:
my $buffer = "";
$stack->push( buffer => \$buffer );
# ...
$stack->pop;
print $buffer;
$stack->push( private => 1 );
# ...
print $stack->pop;
pre_append
A callback, which will be called with a reference to the
"String::BufferStack" object, and the arguments to append, whenever
this stack frame has anything appended to the input buffer, directly
or indirectly.
Within the context of the pre-append callback, "append",
"direct_append", and "set_pre_append" function on the frame the
pre-append is attached to, not the topmost trame. Using "append"
within the pre-append callback is not suggested; use "direct_append"
instead. "set_pre_append" can be used to alter or remove the
pre-append callback itself -- this is not uncommon, in the case
where the first append is the only one which needs be watched for,
for instance.
filter
A callback, used to process data which is appended to the stack
frame. By default, filters are lazy, being called only when a frame
is popped. They can be forced at any time by calling
"flush_filters", however.
depth
Returns the current depth of the stack. This starts at 0, when no frames
have been pushed, and increases by one for each frame pushed.
append STRING [, STRING, ...]
Appends the given strings to the input side of the topmost buffer. This
will call all pre-append hooks attached to it, as well. Note that if the
frame has a filter, the filter will not immediately run, but will be
delayed until the frame is "pop"'d, or "flush_filters" is called.
When called with no frames on the stack, appends the stringins directly
to the "output_buffer".
direct_append STRING [, STRING, ...]
Similar to "append", but appends the strings to the output side of the
frame, skipping pre-append callbacks and filters.
When called with no frames on the stack, appends the strings directly to
the "output_buffer".
pop
Removes the topmost frame on the stack, flushing the topmost filters in
the process. Returns the output buffer of the frame -- note that this
may not contain only strings appended in the current frame, but also
those from before, as a speed optimization. That is:
$stack->append("one");
$stack->push;
$stack->append(" two");
$stack->pop; # returns "one two"
This operation is a no-op if there are no frames on the stack.
set_pre_append CALLBACK
Alters the pre-append callback on the topmost frame. The callback will
be called before text is appended to the input buffer of the frame, and
will be passed the "String::BufferStack" and the arguments to "append".
set_filter FILTER
Alters the filter on the topmost frame. Doing this flushes the filters
on the topmost frame.
filter
Filters the topmost stack frame, if it has outstanding unfiltered data.
This will propagate content to lower frames, possibly calling their
pre-append hooks.
flush
If there are no frames on the stack, calls "flush_output". Otherwise,
calls "flush_filters".
flush_filters
Flushes all filters. This does not flush output from the output buffer;
see "flush_output".
buffer
Returns the contents of the output buffer of the topmost frame; if there
are no frames, returns the output buffer.
buffer_ref
Returns a reference to the output buffer of the topmost frame; if there
are no frames, returns a reference to the output buffer. Note that
adjusting this skips pre-append and filter hooks.
length
Returns the number of characters appended to the current frame; if there
are no frames, returns the length of the output buffer.
flush_output
Flushes all filters using "flush_filters", then flushes output from the
output buffer, using the configured "out_method".
output_buffer
Returns the pending output buffer, which sits below all existing frames.
output_buffer_ref
Returns a reference to the pending output buffer, allowing you to modify
it.
clear
Clears *all* buffers in the stack, including the output buffer.
clear_top
Clears the topmost buffer in the stack; if there are no frames on the
stack, clears the output buffer.
out_method [CALLBACK]
Gets or sets the output method callback, which is given content from the
pending output buffer, which sits below all frames.
SEE ALSO
Many concepts were originally taken from HTML::Mason's internal buffer
stack.
AUTHORS
Alex Vandiver "alexmv@bestpractical.com"
LICENSE
Copyright 2008-2009, Best Practical Solutions.
This package is distributed under the same terms as Perl itself.
