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