package asm
// Metadata contains metadata about an instruction.
type Metadata struct {
head *metaElement
}
type metaElement struct {
next *metaElement
key, value interface{}
}
// Find the element containing key.
//
// Returns nil if there is no such element.
func (m *Metadata) find(key interface{}) *metaElement {
for e := m.head; e != nil; e = e.next {
if e.key == key {
return e
}
}
return nil
}
// Remove an element from the linked list.
//
// Copies as many elements of the list as necessary to remove r, but doesn't
// perform a full copy.
func (m *Metadata) remove(r *metaElement) {
current := &m.head
for e := m.head; e != nil; e = e.next {
if e == r {
// We've found the element we want to remove.
*current = e.next
// No need to copy the tail.
return
}
// There is another element in front of the one we want to remove.
// We have to copy it to be able to change metaElement.next.
cpy := &metaElement{key: e.key, value: e.value}
*current = cpy
current = &cpy.next
}
}
// Set a key to a value.
//
// If value is nil, the key is removed. Avoids modifying old metadata by
// copying if necessary.
func (m *Metadata) Set(key, value interface{}) {
if e := m.find(key); e != nil {
if e.value == value {
// Key is present and the value is the same. Nothing to do.
return
}
// Key is present with a different value. Create a copy of the list
// which doesn't have the element in it.
m.remove(e)
}
// m.head is now a linked list that doesn't contain key.
if value == nil {
return
}
m.head = &metaElement{key: key, value: value, next: m.head}
}
// Get the value of a key.
//
// Returns nil if no value with the given key is present.
func (m *Metadata) Get(key interface{}) interface{} {
if e := m.find(key); e != nil {
return e.value
}
return nil
}