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One reader pointed out that the example isn't compelling because &age would have worked just as well. This CL changes the example to use a nontrivial expression. Don't nitpick the arithmetic. For #45624 Change-Id: Icc745f5ee7000c1d3559da1388c6a5596c4d1f46 Reviewed-on: https://go-review.googlesource.com/c/go/+/714040 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Auto-Submit: Alan Donovan <adonovan@google.com> Reviewed-by: Robert Griesemer <gri@google.com>
32 lines
881 B
Markdown
32 lines
881 B
Markdown
## Changes to the language {#language}
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<!-- https://go.dev/issue/45624 --->
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The built-in `new` function, which creates a new variable, now allows
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its operand to be an expression, specifying the initial value of the
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variable.
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This feature is particularly useful when working with serialization
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packages such as `encoding/json` or protocol buffers that use a
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pointer to represent an optional value, as it enables an optional
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field to be populated in a simple expression, for example:
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```go
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import "encoding/json"
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type Person struct {
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Name string `json:"name"`
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Age *int `json:"age"` // age if known; nil otherwise
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}
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func personJSON(name string, born time.Time) ([]byte, error) {
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return json.Marshal(Person{
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Name: name,
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Age: new(yearsSince(born)),
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})
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}
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func yearsSince(t time.Time) int {
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return int(time.Since(t).Hours() / (365.25 * 24)) // approximately
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}
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```
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