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fmt: explain how Formatter interface affects verbs and flags #39860

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fmt: explain how Formatter interface affects verbs and flags #39860

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85195df
Better explanation of Formatter interface
bboreham Jun 25, 2020
3fa21a2
Rename Format() verb argument for clarity
bboreham Aug 9, 2020
6571b49
Reworded more concisely
bboreham Oct 12, 2020
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3 changes: 2 additions & 1 deletion src/fmt/doc.go
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Expand Up @@ -150,7 +150,8 @@
concrete value that it holds, and printing continues with the next rule.

2. If an operand implements the Formatter interface, it will
be invoked. Formatter provides fine control of formatting.
be invoked. In this case the interpretation of verbs and flags is
controlled by that implementation.

3. If the %v verb is used with the # flag (%#v) and the operand
implements the GoStringer interface, that will be invoked.
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8 changes: 4 additions & 4 deletions src/fmt/print.go
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Expand Up @@ -47,11 +47,11 @@ type State interface {
Flag(c int) bool
}

// Formatter is the interface implemented by values with a custom formatter.
// The implementation of Format may call Sprint(f) or Fprint(f) etc.
// to generate its output.
// Formatter is implemented by any value that has a Format method.
// The implementation controls how State and rune are interpreted,
// and may call Sprint(f) or Fprint(f) etc. to generate its output.
type Formatter interface {
Format(f State, c rune)
Format(f State, verb rune)
}

// Stringer is implemented by any value that has a String method,
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