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package dstream
import "fmt"
// MutateFunc is a function that can be used to change the values of a variable in-place.
type MutateFunc func(interface{})
type mutated struct {
xform
// The name of the variable to be mutated
vname string
// The position of the variable to be mutated
vpos int
// The function that performs the mutation
f MutateFunc
}
// Mutate returns a Dstream in which the variable with the given name
// is transformed using the given function.
func Mutate(ds Dstream, name string, f MutateFunc) Dstream {
// Find the variable's position
vpos := -1
for j, n := range ds.Names() {
if n == name {
vpos = j
break
}
}
if vpos == -1 {
msg := fmt.Sprintf("Mutate: variable '%s' not found", name)
panic(msg)
}
m := &mutated{
xform: xform{
source: ds,
},
vname: name,
vpos: vpos,
f: f,
}
return m
}
func (m *mutated) Next() bool {
if !m.source.Next() {
return false
}
// Call the mutating function on the variable to be
// transformed.
m.f(m.GetPos(m.vpos))
return true
}
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