Module std

Lua Standard Libraries.

This module contains a selection of improved Lua core functions, among others.

Also, after requiring this module, simply referencing symbols in the submodule hierarchy will load the necessary modules on demand.

By default there are no changes to any global symbols, or monkey patching of core module tables and metatables. However, sometimes it's still convenient to do that: For example, when using stdlib from the REPL, or in a prototype where you want to throw caution to the wind and compatibility with other modules be damned. In that case, you can give stdlib permission to scribble all over your namespaces by using the various monkey_patch calls in the library.

Functions

assert (expect[, f=""[, ...]]) Enhance core assert to also allow formatted arguments.
barrel ([namespace=_G]) A barrel of monkey_patches.
elems (t) An iterator over all elements of a sequence.
eval (s) Evaluate a string as Lua code.
getmetamethod (x, n) Return named metamethod, if any, otherwise nil.
ielems (t) An iterator over the integer keyed elements of a sequence.
ipairs (t) An iterator over elements of a sequence, until the first nil value.
ireverse (t) Return a new table with element order reversed.
monkey_patch ([namespace=_G]) Overwrite core methods and metamethods with std enhanced versions.
npairs (t) Ordered iterator for integer keyed values.
pairs (t) Enhance core pairs to respect __pairs even in Lua 5.1.
require (module[, min[, too_big[, pattern]]]) Enhance core require to assert version number compatibility.
ripairs (t) An iterator like ipairs, but in reverse.
rnpairs (t) An iterator like npairs, but in reverse.
tostring (x) Enhance core tostring to render table contents as a string.

Tables

std Module table.

Metamethods

__index (name) Lazy loading of stdlib modules.


Functions

Methods
assert (expect[, f=""[, ...]])
Enhance core assert to also allow formatted arguments.

Parameters:

  • expect expression, expected to be truthy
  • f string format string (default "")
  • ... arguments to format (optional)

Returns:

    value of expect, if truthy

Usage:

     std.assert (expected ~= nil, "100% unexpected!")
 std.assert (expected ~= nil, "%s unexpected!", expected)
barrel ([namespace=_G])
A barrel of monkey_patches.

Apply all monkey_patch functions. Additionally, for backwards compatibility only, write a selection of sub-module functions into the given namespace.

Parameters:

  • namespace table where to install global functions (default _G)

Returns:

    table module table

Usage:

    local std = require "std".barrel ()
elems (t)
An iterator over all elements of a sequence. If t has a __pairs metamethod, use that to iterate.

Parameters:

Returns:

  1. function iterator function
  2. table t, the table being iterated over
  3. key, the previous iteration key

See also:

Usage:

    for value in std.elems {a = 1, b = 2, c = 5} do process (value) end
eval (s)
Evaluate a string as Lua code.

Parameters:

Returns:

    result of evaluating s

Usage:

    std.eval "math.min (2, 10)"
getmetamethod (x, n)
Return named metamethod, if any, otherwise nil.

Parameters:

  • x item to act on
  • n string name of metamethod to lookup

Returns:

    function or nil metamethod function, or nil if no metamethod

Usage:

    lookup = std.getmetamethod (require "std.object", "__index")
ielems (t)
An iterator over the integer keyed elements of a sequence. If t has a __len metamethod, iterate up to the index it returns.

Parameters:

Returns:

  1. function iterator function
  2. table t, the table being iterated over
  3. int index, the previous iteration index

See also:

Usage:

    for v in std.ielems {"a", "b", "c"} do process (v) end
ipairs (t)
An iterator over elements of a sequence, until the first nil value.

Like Lua 5.1 and 5.3, but unlike Lua 5.2 (which looks for and uses the __ipairs metamethod), this iterator returns successive key-value pairs with integer keys starting at 1, up to the first nil valued pair.

Parameters:

Returns:

  1. function iterator function
  2. table t, the table being iterated over
  3. int index, the previous iteration index

See also:

Usage:

     -- length of sequence
 args = {"first", "second", nil, "last"}
 --> 1=first
 --> 2=second
 for i, v in std.ipairs (args) do
   print (string.format ("%d=%s", i, v))
 end
ireverse (t)
Return a new table with element order reversed. Apart from the order of the elments returned, this function follows the same rules as ipairs for determining first and last elements.

Parameters:

Returns:

    table a new table with integer keyed elements in reverse order with respect to t

See also:

Usage:

     local rielems = std.functional.compose (std.ireverse, std.ielems)
 for e in rielems (l) do process (e) end
monkey_patch ([namespace=_G])
Overwrite core methods and metamethods with std enhanced versions.

Write all functions from this module, except std.barrel and std.monkey_patch, into the given namespace.

Parameters:

  • namespace table where to install global functions (default _G)

Returns:

    table the module table

Usage:

    local std = require "std".monkey_patch ()
npairs (t)
Ordered iterator for integer keyed values. Like ipairs, but does not stop until the largest integer key.

Parameters:

Returns:

  1. function iterator function
  2. table t

See also:

Usage:

    for i,v in npairs {"one", nil, "three"} do ... end
pairs (t)
Enhance core pairs to respect __pairs even in Lua 5.1.

Parameters:

Returns:

  1. function iterator function
  2. table t, the table being iterated over
  3. key, the previous iteration key

See also:

Usage:

    for k, v in pairs {"a", b = "c", foo = 42} do process (k, v) end
require (module[, min[, too_big[, pattern]]])
Enhance core require to assert version number compatibility. By default match against the last substring of (dot-delimited) digits in the module version string.

Parameters:

  • module string module to require
  • min string lowest acceptable version (optional)
  • too_big string lowest version that is too big (optional)
  • pattern string to match version in module.version or module._VERSION (default: "([%.%d]+)%D*$") (optional)

Usage:

     -- posix.version == "posix library for Lua 5.2 / 32"
 posix = require ("posix", "29")
ripairs (t)
An iterator like ipairs, but in reverse. Apart from the order of the elments returned, this function follows the same rules as ipairs for determining first and last elements.

Parameters:

Returns:

  1. function iterator function
  2. table t
  3. number #t + 1

See also:

Usage:

    for i, v = ripairs (t) do ... end
rnpairs (t)
An iterator like npairs, but in reverse. Apart from the order of the elments returned, this function follows the same rules as npairs for determining first and last elements.

Parameters:

Returns:

  1. function iterator function
  2. table t

See also:

Usage:

    for i,v in rnpairs {"one", nil, "three"} do ... end
tostring (x)
Enhance core tostring to render table contents as a string.

Parameters:

  • x object to convert to string

Returns:

    string compact string rendering of x

Usage:

     -- {1=baz,foo=bar}
 print (std.tostring {foo="bar","baz"})

Tables

std
Module table.

In addition to the functions documented on this page, and a version field, references to other submodule functions will be loaded on demand.

Fields:

  • version release version string

Metamethods

__index (name)
Lazy loading of stdlib modules. Don't load everything on initial startup, wait until first attempt to access a submodule, and then load it on demand.

Parameters:

Returns:

    table or nil the submodule that was loaded to satisfy the missing name, otherwise nil if nothing was found

Usage:

     local std = require "std"
 local prototype = std.object.prototype
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