DockerCLI/vendor/github.com/docker/notary/tuf/utils/stack.go

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package utils
import (
"fmt"
"sync"
)
// ErrEmptyStack is used when an action that requires some
// content is invoked and the stack is empty
type ErrEmptyStack struct {
action string
}
func (err ErrEmptyStack) Error() string {
return fmt.Sprintf("attempted to %s with empty stack", err.action)
}
// ErrBadTypeCast is used by PopX functions when the item
// cannot be typed to X
type ErrBadTypeCast struct{}
func (err ErrBadTypeCast) Error() string {
return "attempted to do a typed pop and item was not of type"
}
// Stack is a simple type agnostic stack implementation
type Stack struct {
s []interface{}
l sync.Mutex
}
// NewStack create a new stack
func NewStack() *Stack {
s := &Stack{
s: make([]interface{}, 0),
}
return s
}
// Push adds an item to the top of the stack.
func (s *Stack) Push(item interface{}) {
s.l.Lock()
defer s.l.Unlock()
s.s = append(s.s, item)
}
// Pop removes and returns the top item on the stack, or returns
// ErrEmptyStack if the stack has no content
func (s *Stack) Pop() (interface{}, error) {
s.l.Lock()
defer s.l.Unlock()
l := len(s.s)
if l > 0 {
item := s.s[l-1]
s.s = s.s[:l-1]
return item, nil
}
return nil, ErrEmptyStack{action: "Pop"}
}
// PopString attempts to cast the top item on the stack to the string type.
// If this succeeds, it removes and returns the top item. If the item
// is not of the string type, ErrBadTypeCast is returned. If the stack
// is empty, ErrEmptyStack is returned
func (s *Stack) PopString() (string, error) {
s.l.Lock()
defer s.l.Unlock()
l := len(s.s)
if l > 0 {
item := s.s[l-1]
if item, ok := item.(string); ok {
s.s = s.s[:l-1]
return item, nil
}
return "", ErrBadTypeCast{}
}
return "", ErrEmptyStack{action: "PopString"}
}
// Empty returns true if the stack is empty
func (s *Stack) Empty() bool {
s.l.Lock()
defer s.l.Unlock()
return len(s.s) == 0
}