E0017#
The usage of identifier is ambiguous. If it refers to the loop variable, please
use as <id>
to bind it in the pattern. If it refers to the original value of
the variable before entering the loop, please bind it to a new binder outside
the loop.
错误示例#
fn main {
let a : @string.View = "asdf"
loop a {
[_, .. d] => {
println(a)
// ^
// Warning: The usage of 'a' is ambiguous. If it refers to the loop
// variable, please use `as a` to bind it in the pattern. If it refers to
// the original value of 'a' before entering the loop, please bind it to a
// new binder outside the loop.
continue d
}
[] => ()
}
}
The output is:
asdf
asdf
asdf
asdf
Because a
refers to the value of a
before entering the loop, therefore the
value is always the same.
建议#
It is often the case that you may want to refer to the loop variable that
changes with loop iterations. If so, use as <id>
to bind it in the pattern.
fn main {
let a : @string.View = "asdf"
loop a {
[_, .. d] as a => {
println(a)
continue d
}
[] => ()
}
}
Output:
asdf
sdf
df
f
Or, if you want to refer to the original value of the variable before entering the loop, explicitly bind it to another name outside the loop.
fn main {
let a : @string.View = "asdf"
let b = a
loop a {
[_, .. d] => {
println(b)
continue d
}
[] => ()
}
}
Output:
asdf
asdf
asdf
asdf