PHP8 —— New String Helpers

新增了三个字符串函数，str_starts_with, str_ends_with, str_contains， PHP 的函数这么方便，很难想象竟然一直没有这几个。 str_starts_with 判断字符串是否以另一个字符串开头，在PHP7以及之前 $id = 'inv_abcdefgh'; $result = strpos($id, 'inv_') === 0; var_dump($result); // true PHP8 中可以直接这么写 $result = str_starts_with($id, 'inv_'); str_ends_with 判断字符串是否以另外一个字符串结尾，在 PHP7 及之前，比较麻烦，通常是这么写 $id = 'abcd_inv'; $result = strpos(strrev($id), strrev('_inv')) === 0; 或者 $result = substr($id, -1 * strlen('_inv')) === '_inv'; 或者上正则吧 $result = preg_match('/_inv$/', $id) === 1; 看起来都是比较麻烦的。PHP8 里面可以简化成下面这样了 $id = 'abcd_inv'; $result = str_ends_with($id, '_ind'); str_contains 字符串包含，PHP8 之前一般就是 strpos 来实现了 $url = 'https://example?for=bar'; $result = strpos($url, '?') !== FALSE; PHP8 就直接一点 $result = str_contains($url, '?');
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Fold function in haskell

let’s first take a look at some list functions, and see what’s the characteristic they all share

  • sum: computes the sum of the numbers of a structure;
  • and: returns the conjunction of a container of Bools;
  • map: map f xs is the list obtained by applying f to each element of xs.

There three are all common list function, and act very differently, but can be defined recursively using pattern matching as follow:

mySum :: (Num t) => [t] -> t
mySum []       = 0              -- sum of empty is 0
mySum (x : xs) = x + mySum xs   -- otherwise, add first element to sum of rest of the list

myAnd :: [Bool] -> Bool
myAnd [] = True                 -- and of empty is True
myAnd (x : xs) = x && myAnd xs  -- otherwise, return the conjunction of first element and the rest of list

myMap :: (t -> t) -> [t] -> [t]
myMap _ []       = []               -- map any function to empty is empty
myMap f (x : xs) = f x : myMap f xs -- otherwise, prepends f of first element to map f of rest of list

Here we can see the common pattern: Each of them has a binary operator, a starting value (typically the right-identity of the operator), and a list:

  • in sum function, they are +, 0 and the list;
  • in and function, they are &&, True and the list;
  • in map function, things is a litter complicate, but we can still find them: (\x xs -> (f x):xs), [] and the the list.

In Haskell, we have a high order function which applied to a binary operator, a starting value (typically the right-identity of the operator), and a list, reduces the list using the binary operator, from right to left:

foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)

So we can rewrite sum, and and map use foldr like this:

mySum' :: (Num t) => [t] -> t
mySum' xs = foldr (+) 0 xs

myAnd' :: [Bool] -> Bool
myAnd' xs = foldr (&&) True xs

myMap' :: (t -> t) -> [t] -> [t]
myMap' xs = foldr (\x xs -> (f x):xs) [] xs

It’s way much easier for us to understand.
That’s all for today, happy coding!

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