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86 lines
2 KiB
Markdown
86 lines
2 KiB
Markdown
[](https://goreportcard.com/report/github.com/go-toolsmith/astcast)
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[](https://godoc.org/github.com/go-toolsmith/astcast)
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# astcast
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Package astcast wraps type assertion operations in such way that you don't have
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to worry about nil pointer results anymore.
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## Installation
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```bash
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go get -v github.com/go-toolsmith/astcast
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```
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## Example
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```go
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package main
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import (
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"fmt"
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"github.com/go-toolsmith/astcast"
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"github.com/go-toolsmith/strparse"
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)
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func main() {
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x := strparse.Expr(`(foo * bar) + 1`)
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// x type is ast.Expr, we want to access bar operand
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// that is a RHS of the LHS of the addition.
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// Note that addition LHS (X field) is has parenthesis,
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// so we have to remove them too.
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add := astcast.ToBinaryExpr(x)
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mul := astcast.ToBinaryExpr(astcast.ToParenExpr(add.X).X)
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bar := astcast.ToIdent(mul.Y)
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fmt.Printf("%T %s\n", bar, bar.Name) // => *ast.Ident bar
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// If argument has different dynamic type,
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// non-nil sentinel object of requested type is returned.
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// Those sentinel objects are exported so if you need
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// to know whether it was a nil interface value of
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// failed type assertion, you can compare returned
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// object with such a sentinel.
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y := astcast.ToCallExpr(strparse.Expr(`x`))
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if y == astcast.NilCallExpr {
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fmt.Println("it is a sentinel, type assertion failed")
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}
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}
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```
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Without `astcast`, you would have to do a lots of type assertions:
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```go
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package main
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import (
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"fmt"
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"github.com/go-toolsmith/strparse"
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)
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func main() {
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x := strparse.Expr(`(foo * bar) + 1`)
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add, ok := x.(*ast.BinaryExpr)
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if !ok || add == nil {
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return
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}
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additionLHS, ok := add.X.(*ast.ParenExpr)
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if !ok || additionLHS == nil {
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return
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}
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mul, ok := additionLHS.X.(*ast.BinaryExpr)
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if !ok || mul == nil {
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return
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}
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bar, ok := mul.Y.(*ast.Ident)
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if !ok || bar == nil {
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return
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}
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fmt.Printf("%T %s\n", bar, bar.Name)
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}
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```
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