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utils.php
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Sat, May 24, 01:39

utils.php
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<?php
/*
* Copyright 2011 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
function id($x) {
return $x;
}
function idx(array $array, $key, $default = null) {
return array_key_exists($key, $array) ? $array[$key] : $default;
}
function mpull(array $list, $method, $key_method = null) {
$result = array();
foreach ($list as $key => $object) {
if ($key_method !== null) {
$key = $object->$key_method();
}
if ($method !== null) {
$value = $object->$method();
} else {
$value = $object;
}
$result[$key] = $value;
}
return $result;
}
function ipull(array $list, $index, $key_index = null) {
$result = array();
foreach ($list as $key => $array) {
if ($key_index !== null) {
$key = $array[$key_index];
}
if ($index !== null) {
$value = $array[$index];
} else {
$value = $array;
}
$result[$key] = $value;
}
return $result;
}
function mgroup(array $list, $by /*, ... */) {
$map = mpull($list, $by);
$groups = array();
foreach ($map as $group) {
// Can't array_fill_keys() here because 'false' gets encoded wrong.
$groups[$group] = array();
}
foreach ($map as $key => $group) {
$groups[$group][$key] = $list[$key];
}
$args = func_get_args();
$args = array_slice($args, 2);
if ($args) {
array_unshift($args, null);
foreach ($groups as $group_key => $grouped) {
$args[0] = $grouped;
$groups[$group_key] = call_user_func_array('mgroup', $args);
}
}
return $groups;
}
/**
* Sort a list of objects by the return value of some method.
*/
function msort(array $list, $method) {
$surrogate = mpull($list, $method);
asort($surrogate);
$result = array();
foreach ($surrogate as $key => $value) {
$result[$key] = $list[$key];
}
return $result;
}
/**
* Selects a list of keys from an array, returning a new array with only the
* key-value pairs identified by the selected keys, in the specified order.
*
* Note that since this function orders keys in the result according to the
* order they appear in the list of keys, there are effectively two common
* uses: either reducing a large dictionary to a smaller one, or changing the
* key order on an existing dictionary.
*
* @param dict Dictionary of key-value pairs to select from.
* @param list List of keys to select.
* @return dict Dictionary of only those key-value pairs where the key was
* present in the list of keys to select. Ordering is
* determined by the list order.
*/
function array_select_keys(array $dict, array $keys) {
$result = array();
foreach ($keys as $key) {
if (array_key_exists($key, $dict)) {
$result[$key] = $dict[$key];
}
}
return $result;
}
/**
* Returns the first argument which is not strictly null, or `null' if there
* are no such arguments. Identical to the MySQL function of the same name.
*
* @param ... Zero or more arguments of any type.
* @return mixed First non-null arg, or null if no such arg exists.
*/
function coalesce(/* ... */) {
$args = func_get_args();
foreach ($args as $arg) {
if ($arg !== null) {
return $arg;
}
}
return null;
}
/**
* Similar to coalesce(), but less strict: returns the first non-empty()
* argument, instead of the first argument that is strictly nonnull. If no
* argument is nonempty, it returns the last argument. This is useful
* idiomatically for setting defaults:
*
* $value = nonempty($get_value, 0);
*
* @param ... Zero or more arguments of any type.
* @return mixed First non-empty() arg, or last arg if no such arg
* exists, or null if you pased in zero args.
*/
function nonempty(/* ... */) {
$args = func_get_args();
foreach ($args as $arg) {
if ($arg) {
break;
}
}
return $arg;
}
/**
* Invokes the "new" operator with a vector of arguments. There is no way to
* call_user_func_array() on a class constructor, so you can instead use this
* function:
*
* $obj = newv($class_name, $argv);
*
* That is, these two statements are equivalent:
*
* $pancake = new Pancake('Blueberry', 'Maple Syrup', true);
* $pancake = newv('Pancake', array('Blueberry', 'Maple Syrup', true));
*
* DO NOT solve this problem in other, more creative ways! Two popular
* alternatives are:
*
* - Build a fake serialized object and unserialize it.
* - Invoke the constructor twice.
*
* These are really bad solutions to the problem because they can have side
* effects (e.g., __wakeup()) and give you an object in an otherwise impossible
* state! Please endeavor to keep your objects in possible states.
*
* If you own the classes you're doing this for, you should consider whether
* or not restructuring your code (for instance, by creating static
* construction methods) might make it cleaner before using newv(). Static
* construtors can be invoked with call_user_func_array(), and may give your
* class a cleaner and more descriptive API.
*
* @param string The name of a class.
* @param list Array of arguments to pass to its constructor.
*
* @return obj A new object of the specified class, constructed by passing
* the argument vector to its constructor.
*/
function newv($class_name, array $argv) {
$reflector = new ReflectionClass($class_name);
return $reflector->newInstanceArgs($argv);
}

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