Get string from array via property lookup, but insert a variable - php

I want to use property look-up on an associative array of strings, but there's a catch - I need to be able to use a variable in the string. I came up with two solutions, but both seem hacky in PHP.
$foo = [
'someProp' => 'Some value here: $$value$$.'
];
$myProp = 'someProp';
$value = 'some value';
$myString = $foo[$myProp];
$myString = str_replace('$$value$$', $value, $myString);
echo $myString;
In JavaScript, I would probably use functions instead of strings and return the string including the variable. I've heard that this is bad practice in PHP.
$foo = array(
'someProp' => function($value) {
return "Some value here: {$value}.";
}
);
$myProp = 'someProp';
$value = 'some value';
$myString = $foo[$myProp]($value);
echo $myString;
To be sure this is not an X/Y problem, I will say that my goal is to abstract my error messages to one location in my code (the array mentioned here) and form what might be considered an error api for use throughout the application. For example:
try {
something(); //throws "MyException('someProp', 'someValue');
}
catch (MyException $e) {
$someClass->addError($e->getType(), $e->getValue());
//this function will get the string based on $type and add $value to it, then add the message to an array
}
Are either of these two approaches the way to go? The answer I'm looking for would include a more optimum solution if there is one and mature thoughts on my two proposed solutions.

From your example, is there only a single variable per message string or it could be many variables?
If there's only single variable, instead of role out your old string interpolation, you could use sprinf for this. This is more flexible in my opinion since it allows you to do many formatting types e.g. int, decimal etc
$foo = [
'someProp' => 'Some value here: %s.'
];
$myString = sprintf($myString, $value);

Related

Good practice for referencing returned array values

This is something I haven't seen before but it appears to be supported and it does work, referencing the returned array key directly after the providing function is called. BUT... is this good practice? Will this be supported in the future? Does this even have a name?
<?php
function example_function() {
$return = array('part_1', 'part_2');
return $return;
}
$var = example_function()[0];
echo $var;
To get the same result I would normally do the following
$var = example_function();
$var = $var[0];
It's called Array Dereferencing. It has been available since PHP 5.4. It is acceptable to use although some might say it reduces readability.
Use it only when you are sure that you will always get array to work on. Sometimes ago I've have following code in some scraper class:
$ip = $this->getIP()[0];
I didn't check whether this function could return string and it caused some logic errors. Nowadays each time when I want to get array's item I do
$ip = $this->getIP()
if(is_array($ip)) {
$ip = $ip[0];
} else {
throw new Exception('Expects array here')
}

PHP: Specify argument variable names when calling a function?

This might seem like an academic or useless topic, but I'm curious.
When developing web pages with PHP, I often need to call functions that take several arguments. I frequently need to look up the spec for the function (on php.net or in my include files, if it's a function I defined) to remind myself what the variables are and what order they're in and what the defaults are, etc. I imagine many of you can relate to this.
A function defined like this:
function do_something_awesome ($people_array, $places_recordset, $num_cycles, $num_frogs,
$url = '?default=yes', $submit_name = 'default_submit_label') {
...
}
when called, might look like this:
$result = do_something_awesome($names, $rsTowns, $c, $f);
My question is this: I'd like to write my code in a way that reminds me of which argument corresponds to each variable, during function calls like this. Is it ever legal to call a function as follows?
$result = do_something_awesome($people_array = $names, $places_recordset = $rsTowns,
$num_cycles = $c, $num_frogs = $f);
If not in PHP, are there other languages where method calls can be made in this way?
To answer your first question:
My question is this: I'd like to write my code in a way that reminds me of which argument corresponds to each variable, during function calls like this.
AFAIK, many PHP coders do it by passing in an associative array as the only argument. However, you'll have to do your own variables checking inside the called function.
$result = do_something_awesome(array(
'people_array' => $names,
'places_recordset' => $rsTowns,
'num_cycles' => $c,
'num_frogs' => $f
));
As for:
Is it ever legal to call a function as follows?
It won't cause any PHP errors, but what you are effectively doing is:
$result = do_something_awesome( expression, expression, expression, expression );
See: PHP Functions arguments
PHP won't know to put $people_array = ... or $num_frogs = ... in their corresponding places when you decide to switch their order around. Furthermore, as DCoder said, these expressions actually take place in the current scope, and will change any pre-existing variables without letting you know.
What about using an object as the only argument:
function my_function($arguments) {
if (!is_object($arguments)) throw new Exception();
$default_values = array('arg1' => 'value1', 'arg2' => 'value2');
foreach ($default_values as $key => $default_value)
if (!isset($arguments->$key)) $arguments->$key = $default_value;
## do the job ##
}
## and then
$my_arguments = new stdClass();
$my_arguments->arg2 = 'some_value';
my_function($my_arguments);
You can try this out:
$bas = 'This is passed to the function.';
$bar = 'This will be modified.';
function foo($bar)
{
echo $bar;
}
foo($bar = $bas);
echo $bar;
The output from this script would be 'This is passed to the function.This is passed to the function.'. So like DCoder said, while you can use them and it's perfectly legal but if you had other variables with the same name as the function arguments, this will overwrite them (in this case the original $bar was overwritten).

Using variables in preg_replace

i have following string in $subject variable
<p>{{headline}}</p>
And i have a variable$headline="Hello World"
As you guess i want to replace {{headline}} With Hello World using preg-replace.
Method must be dynamic, because it's just an example for headline.
$vars = array(
'headline' => 'foo'
);
echo preg_replace_callback('/\{\{(\w+)\}\}/', function (array $m) use ($vars) {
return $vars[$m[1]];
}, '<p>{{headline}}</p>');
You might really want to look into an existing templating system with a similar syntax but based on a proper parser though, like http://twig.sensiolabs.org. Mustache also basically already does the same thing.

Setting PHP multidimensional session variable in function

Say I have a function called set_session_variable that looks like:
function set_session_variable($name, $value) {
// ...write value to the specified path
}
How would I write this function (without using an eval) so that I can do something like:
set_session_variable('foo', 'bar'); // Would set $_SESSION['foo'] = 'bar';
set_session_variable('foo[bar][baz]', 'blah'); // Would set $_SESSION['foo']['bar']['baz'] = 'blah';
I highly suggest, that you won't use
set_session_variable('foo[bar][baz]', 'blah');
but instead
set_session_variable('foo', array('bar'=>array('baz' => 'blah')));
Additionally, you don't need a function call for that at all:
$_SESSION['foo']['bar']['baz'] = 'blah';
You can change the implementation of $_SESSION with the session save handler.
If you're only concerned how you could parse a string like 'foo[bar][baz]', this has been asked before, for example use strings to access (potentially large) multidimensional arrays.
A more relevant question is why you need a function at all. Function calls have a cost, and the function doesn't appear to do useful work.
Example assignments:
$_SESSION['foo'] = 'bar';
$_SESSION['foo']['bar']['baz'] = 'blah';
$foo['bar']['baz'] = 'blah';
$_SESSION['foo'] = $foo;
In direct answer to your question: You could parse the value of $name within set_session_variable() using the PCRE module and a regular expression.
Even simpler and faster would be parsing it with sscanf() provided you are able and willing to impose a convention on the naming of array keys.
A cleaner alternative function:
$array['bar']['baz'] = 'blah';
set_session_variable('foo', $array);
function set_session_variable($key, $val) {
$_SESSION[$key] = $val;
}
One way to solve this is to mimic function overloading, example in this post -> PHP function overloading
Another way is to add one string argument to your function, with your array indices delimited.
For example: set_session_variable('foo', 'bar', 'baz;key');
Which saves the value 'bar' into foo['baz']['key'].
All you have to do is tear the 3rd argument apart (i use ; as delimiter here).

PHP: Variable in a function name

I want to trigger a function based on a variable.
function sound_dog() { return 'woof'; }
function sound_cow() { return 'moo'; }
$animal = 'cow';
print sound_{$animal}(); *
The * line is the line that's not correct.
I've done this before, but I can't find it. I'm aware of the potential security problems, etc.
Anyone? Many thanks.
You can do that, but not without interpolating the string first:
$animfunc = 'sound_' . $animal;
print $animfunc();
Or, skip the temporary variable with call_user_func():
call_user_func('sound_' . $animal);
You can do it like this:
$animal = 'cow';
$sounder = "sound_$animal";
print ${sounder}();
However, a much better way would be to use an array:
$sounds = array('dog' => sound_dog, 'cow' => sound_cow);
$animal = 'cow';
print $sounds[$animal]();
One of the advantages of the array method is that when you come back to your code six months later and wonder "gee, where is this sound_cow function used?" you can answer that question with a simple text search instead of having to follow all the logic that creates variable function names on the fly.
http://php.net/manual/en/functions.variable-functions.php
To do your example, you'd do
$animal_function = "sound_$animal";
$animal_function();
You can use curly brackets to build your function name. Not sure of backwards compatibility, but at least PHP 7+ can do it.
Here is my code when using Carbon to add or subtract time based on user chosen type (of 'add' or 'sub'):
$type = $this->date->calculation_type; // 'add' or 'sub'
$result = $this->contactFields[$this->date->{'base_date_field'}]
->{$type.'Years'}( $this->date->{'calculation_years'} )
->{$type.'Months'}( $this->date->{'calculation_months'} )
->{$type.'Weeks'}( $this->date->{'calculation_weeks'} )
->{$type.'Days'}( $this->date->{'calculation_days'} );
The important part here is the {$type.'someString'} sections. This will generate the function name before executing it. So in the first case if the user has chosen 'add', {$type.'Years'} becomes addYears.
For PHP >= 7 you can use this way:
function sound_dog() { return 'woof'; }
function sound_cow() { return 'moo'; }
$animal = 'cow';
print ("sound_$animal")();
You should ask yourself why you need to be doing this, perhaps you need to refactor your code to something like the following:
function animal_sound($type){
$animals=array();
$animals['dog'] = "woof";
$animals['cow'] = "moo";
return $animals[$type];
}
$animal = "cow";
print animal_sound($animal);
You can use $this-> and self:: for class-functions. Example provided below with a function input-parameter.
$var = 'some_class_function';
call_user_func(array($this, $var), $inputValue);
// equivalent to: $this->some_class_function($inputValue);
And yet another solution to what I like to call the dog-cow problem. This will spare a lot of superfluous function names and definitions and is perfect PHP syntax and probably future proof:
$animal = 'cow';
$sounds = [
'dog' => function() { return 'woof'; },
'cow' => function() { return 'moo'; }
];
print ($sounds[$animal])();
and looks a little bit less like trickery as the "string to function names" versions.
JavaScript devs might prefer this one for obvious reasons.
(tested on Windows, PHP 7.4.0 Apache 2.4)

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