问题
Is Kotlin ?.let
thread-safe?
Let's say a
variable can be changed in different thread.
Is using a?.let { /* */ }
thread-safe? If it's equal to if (a != null) { block() }
can it happen that in if
it's not null and in block
it's already null?
回答1:
a?.let { block() }
is indeed equivalent to if (a != null) block()
.
This also means that if a
is a mutable variable, then:
a
might be reassigned after the null check and hold anull
value whenblock()
is executed;All concurrency-related effects are in power, and proper synchronization is required if
a
is shared between threads to avoid a race condition;
However, as let { ... }
actually passes its receiver as the single argument to the function it takes, it can be used to capture the value of a
and use it inside the lambda instead of accessing the property again in the block()
. For example:
a?.let { notNullA -> block(notNullA) }
// with implicit parameter `it`, this is equivalent to:
a?.let { block(it) }
Here, the value of a
passed as the argument into the lambda is guaranteed to be the same value that was checked for null. However, observing a
again in the block()
might return a null or a different value, and observing the mutable state of the given instance should also be properly synchronized.
来源:https://stackoverflow.com/questions/57324180/is-kotlin-let-thread-safe