What is the meaning of the nested of squared brackets indicating optional params in php documentation

Question

I know that the square brackets indicate optional parameters in php documentation. Parameters in PHP documentation, squared brackets?

But does the nesting of brackets have any meaning? Are you supposed to resolve the inner-most bracketed parameters first the way you solve for stuff in the inner parenthesis in math?

In other words, are this

string http_build_url ([ mixed $url [, mixed $parts [, int $flags = HTTP_URL_REPLACE [, array &$new_url ]]]] )

and

string http_build_url ([ mixed $url] [, mixed $parts] [, int $flags = HTTP_URL_REPLACE] [, array &$new_url ] )

equivalent?

It just means that you have to have the arguments in order from left to right. If you want to use one of the middle most params, you will need the ones leading up to it. — Justin Wood, Dec 18 '13 at 20:21
Where have you seen the second example in the documentation? — Jonathan Kuhn, Dec 18 '13 at 20:22
@Jessica That specific example they probably made up, however I assume that they have seen that style somewhere or else why the question. — Jonathan Kuhn, Dec 18 '13 at 20:25
Right I'm saying I really doubt they saw it anywhere, I think he made it up completely. — Jessica, Dec 18 '13 at 20:25

hek2mgl · Answer 1 · 2013-12-18T20:39:40.437

2

No, because the , isn't required if only the first param is passed. That's why it is part of the next nested [, param ] declaration.

Example:

function abc($a);      --> [$a]         (just a is optional. no , required)
function abc($a, $b);  --> [$a [, $b]]  (the , is only necessary if you pass $b as well)

Params are nested, because the n+1th param needs the nth param to exist. Meaning you can't pass the second param if you didn't passed the first.

This notation is used across all programming languages and other technical documentation to describe optional arguments. I don't know where it is specified, would appreciate some input on that.

edited Dec 18 '13 at 20:39

answered Dec 18 '13 at 20:22

hek2mgl

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The edit makes this actually make sense, +1 for explaining the comma stuff. – Jessica Dec 18 '13 at 20:26
1

Was harder to explain than to understand :) – hek2mgl Dec 18 '13 at 20:27

score 1 · Answer 2 · answered Dec 18 '13 at 20:21

1

Parameters always go in the order they are listed. You don't "Resolve" parameters.

Read the answers in the question you linked to. It means each one is optional.

answered Dec 18 '13 at 20:21

Jessica

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score 1 · Accepted Answer · answered Dec 18 '13 at 20:27

No, they are not equivalent.

PHP function parameters are strictly positional and function([$1] [,$2] [,3]) implies that you can simply call the function as function($3); which is incorrect.

If you wish to invoke a function with only the third optional argument then it must be called as function( , , $3);

This is why PHP.net's function references are listed as function([$1 [,$2 [,$3]]])

What is the meaning of the nested of squared brackets indicating optional params in php documentation

3 Answers3