Error code E0408
An "or" pattern was used where the variable bindings are not consistently bound across patterns.
Erroneous code example:
ⓘ
Here, y
is bound to the contents of the Some
and can be used within the
block corresponding to the match arm. However, in case x
is None
, we have
not specified what y
is, and the block will use a nonexistent variable.
To fix this error, either split into multiple match arms:
or, bind the variable to a field of the same type in all sub-patterns of the or pattern:
In this example, if x
matches the pattern (0, _)
, the second field is set
to y
. If it matches (_, 0)
, the first field is set to y
; so in all
cases y
is set to some value.