March 2017
Intermediate to advanced
364 pages
9h 45m
Japanese
Content preview from 初めてのPHP
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5.5
引数と返り値への規則の適用
91
5.5
引数と返り値への規則の適用
PHP エンジンに特に指示していない限り、関数の引数と返り値には型や値に関する制約はあり
ません。例 5-9 の
countdown()
関数では引数が数値であるとみなしますが、引数として
"Caramel"
などの文字列を渡すこともでき、PHP エンジンはエラーを発しません。
型宣言は、引数値に関する制約を表す方法です。型宣言は引数に使える値の種類を PHP エンジ
ンに知らせ、正しくない種類を指定したときに警告できるようにします。表5-1 に PHP エンジン
が理解できるさまざまな宣言の種類とそのサポートが導入された PHP バージョンを示します。
表5-1 型宣言
宣言 引数規則 導入バージョン
array
配列に限る 5.1.0
bool
真偽値（
true
か
false
）に限る 7.0.0
callable
呼び出し可能な関数やメソッドを表すものに限る
＊1
5.4.0
float
浮動小数点数に限る 7.0.0
int
整数に限る 7.0.0
string
文字列に限る 7.0.0
クラスの名前 そのクラスのインスタンスに限る（クラスとインスタンスについての詳し
い情報は「6 章データとロジックの結合：オブジェクトの操作」を参照）
5.0.0
関数を定義するときには、引数名の前に関数宣言を記述します。例 5-24 は、例 5-9の関数に
int
型宣言を適切に行っています。
例
5-24
引数型の宣言
function countdown(int $top) ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.