Php references can only be defined in function parameters. Transferring references in real time is forbidden.

{Code...} which scenarios are applicable to the above two situations respectively?

14. The reference can only be defined in function parameters. It is forbidden to pass the reference in real time. For example: // reference defined in function parameters-allowed function defineRefInMethod (& $ a) {$ a = 'a';} defineRefInMethod ($ B); echo $ B; // 'A' // pass the reference in real time-the function callTimePassRef ($ a) {$ a = 'a';} callTimePassRef (& $ c); echo $ c; // 'A'

Which scenarios are applicable to the above two situations?

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14. The reference can only be defined in function parameters. It is forbidden to pass the reference in real time. For example: // reference defined in function parameters-allowed function defineRefInMethod (& $ a) {$ a = 'a';} defineRefInMethod ($ B); echo $ B; // 'A' // pass the reference in real time-the function callTimePassRef ($ a) {$ a = 'a';} callTimePassRef (& $ c); echo $ c; // 'A'

Which scenarios are applicable to the above two situations?

Sometimes, we process arrays like this.

$arr = [...];foreach($arr as &$value){    // do something here...}print_r($arr);

1. The former is the data transfer address, and the latter is the data transfer value. The former generates global changes for & Modified variables in the function body, while the latter does not. A function can have only one return value. Generally, the return value is used when a single variable is changed. You can only use & when changing multiple variables &.
2. References can only be defined in function parameters. This sentence indicates suspicion, does not know where the source is, and the last half of the sentence is incredible.

In fact, the second method will report an error.

If no error is reported, it is also a wonderful way of writing, because the address is read-only and cannot be written.