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Basic Functions
===============
.. module:: fun
The section contains functions to create iterators from Lua objects.
.. function:: iter(array)
iter(map)
iter(string)
iter(gen, param, state)
:returns: ``gen, param, state`` -- :ref:`iterator triplet <iterator_triplet>`
Make ``gen, param, state`` iterator from the iterable object.
The function is a generalized version of :func:`pairs` and :func:`ipairs`.
The function distinguish between arrays and maps using ``#arg == 0``
check to detect maps. For arrays ``ipairs`` is used. For maps a modified
version of ``pairs`` is used that also returns keys. Userdata objects
are handled in the same way as tables.
If ``LUAJIT_ENABLE_LUA52COMPAT`` [#luajit_lua52compat]_ mode is enabled and
argument has metamethods ``__pairs`` (for maps) or ``__ipairs`` for (arrays),
call it with the table or userdata as argument and return the first three
results from the call [#lua52_ipairs]_.
All library iterator are suitable to use with Lua's ``for .. in`` loop.
.. code-block:: lua
> for _it, a in iter({1, 2, 3}) do print(a) end
1
2
3
> for _it, k, v in iter({ a = 1, b = 2, c = 3}) do print(k, v) end
b 2
a 1
c 3
> for _it, a in iter("abcde") do print(a) end
a
b
c
d
e
The first cycle variable *_it* is needed to store an internal state of
the iterator. The value must be always ignored in loops:
.. code-block:: lua
for _it, a, b in iter({ a = 1, b = 2, c = 3}) do print(a, b) end
-- _it is some internal iterator state - always ignore it
-- a, b are values return from the iterator
Simple iterators like ``iter({1, 2, 3})`` have simple states, whereas
other iterators like :func:`zip` or :func:`chain` have complicated
internal states which values senseless for the end user.
Check out :doc:`under_the_hood` section for more details.
There is also the possibility to supply custom iterators to the
function:
.. code-block:: lua
> local function mypairs_gen(max, state)
if (state >= max) then
return nil
end
return state + 1, state + 1
end
> local function mypairs(max)
return mypairs_gen, max, 0
end
> for _it, a in iter(mypairs(10)) do print(a) end
1
2
3
4
5
6
7
8
9
10
Iterators can return multiple values.
Check out :doc:`under_the_hood` section for more details.
.. [#luajit_lua52compat] http://luajit.org/extensions.html
.. [#lua52_ipairs] http://www.lua.org/manual/5.2/manual.html#pdf-ipairs
.. function:: each(fun, gen, param, state)
iterator:each(fun)
:returns: none
Execute the *fun* for each iteration value. The function is equivalent to
the code below:
.. code-block:: lua
for _it, ... in iter(gen, param, state) do
fun(...)
end
Examples:
.. code-block:: lua
> each(print, { a = 1, b = 2, c = 3})
b 2
a 1
c 3
> each(print, {1, 2, 3})
1
2
3
The function is used for its side effects. Implementation directly applies
*fun* to all iteration values without returning a new iterator, in contrast
to functions like :func:`map`.
.. seealso:: :func:`map`, :func:`reduce`
.. function:: for_each(fun, gen, param, state)
iterator:for_each(fun)
An alias for :func:`each`.
.. function:: foreach(fun, gen, param, state)
iterator:foreach(fun)
An alias for :func:`each`.
|
