Mixing
What do underscores mean in anonymous functions?
I have the method below which I am trying to understand
def method1[A](
messageCallback: String => A,
failureCallback: Throwable => Unit = (_: Throwable) => Unit
) = {}
What does the (_: Throwable) => Unit) mean?
I understand that it's the default function literal but I don't understand the underscore.
scala lambda functional-programming anonymous-function
edited Jan 3 at 1:34
Andrey Tyukin
30.2k42351
asked Jan 2 at 17:07
CrtCrt
2,39822636
add a comment |
I have the method below which I am trying to understand
def method1[A](
messageCallback: String => A,
failureCallback: Throwable => Unit = (_: Throwable) => Unit
) = {}
What does the (_: Throwable) => Unit) mean?
I understand that it's the default function literal but I don't understand the underscore.
scala lambda functional-programming anonymous-function
edited Jan 3 at 1:34
Andrey Tyukin
30.2k42351
asked Jan 2 at 17:07
CrtCrt
2,39822636
2
_means anything. In this case in particular the idea is, given any parameter just ignore it. And the body of the function just returns Unit - in other words the default is an empty callback that does nothing rewarding of the value passed to the callback function.
– Luis Miguel Mejía Suárez
Jan 2 at 17:42
add a comment |
I have the method below which I am trying to understand
def method1[A](
messageCallback: String => A,
failureCallback: Throwable => Unit = (_: Throwable) => Unit
) = {}
What does the (_: Throwable) => Unit) mean?
I understand that it's the default function literal but I don't understand the underscore.
scala lambda functional-programming anonymous-function
edited Jan 3 at 1:34
Andrey Tyukin
30.2k42351
asked Jan 2 at 17:07
CrtCrt
2,39822636
I have the method below which I am trying to understand
def method1[A](
messageCallback: String => A,
failureCallback: Throwable => Unit = (_: Throwable) => Unit
) = {}
What does the (_: Throwable) => Unit) mean?
I understand that it's the default function literal but I don't understand the underscore.
scala lambda functional-programming anonymous-function
scala lambda functional-programming anonymous-function
edited Jan 3 at 1:34
Andrey Tyukin
30.2k42351
asked Jan 2 at 17:07
CrtCrt
2,39822636
edited Jan 3 at 1:34
Andrey Tyukin
30.2k42351
asked Jan 2 at 17:07
CrtCrt
2,39822636
edited Jan 3 at 1:34
Andrey Tyukin
30.2k42351
edited Jan 3 at 1:34
Andrey Tyukin
30.2k42351
edited Jan 3 at 1:34
Andrey Tyukin
30.2k42351
30.2k42351
asked Jan 2 at 17:07
CrtCrt
2,39822636
asked Jan 2 at 17:07
CrtCrt
2,39822636
asked Jan 2 at 17:07
CrtCrt
2,39822636
2,39822636
2
_means anything. In this case in particular the idea is, given any parameter just ignore it. And the body of the function just returns Unit - in other words the default is an empty callback that does nothing rewarding of the value passed to the callback function.
– Luis Miguel Mejía Suárez
Jan 2 at 17:42
add a comment |
2
_means anything. In this case in particular the idea is, given any parameter just ignore it. And the body of the function just returns Unit - in other words the default is an empty callback that does nothing rewarding of the value passed to the callback function.
– Luis Miguel Mejía Suárez
Jan 2 at 17:42
2
2
_ means anything. In this case in particular the idea is, given any parameter just ignore it. And the body of the function just returns Unit - in other words the default is an empty callback that does nothing rewarding of the value passed to the callback function.– Luis Miguel Mejía Suárez
Jan 2 at 17:42
_ means anything. In this case in particular the idea is, given any parameter just ignore it. And the body of the function just returns Unit - in other words the default is an empty callback that does nothing rewarding of the value passed to the callback function.– Luis Miguel Mejía Suárez
Jan 2 at 17:42
add a comment |
1 Answer
1
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oldest
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It's a default implementation of a function. It's so simple that its signature looks almost the same as implementation itself; its signature is Throwable => Unit, and it is implemented with the trivial body (_: Throwable) => Unit. It means "take some Throwable at input and just don't return anything".
It's the same as implementing it as (a: Throwable) => Unit, but then compiler would complain that a is unused.
Another alternative for the same thing is (a: Throwable) => ().
answered Jan 2 at 17:42
sloucslouc
5,7542829
add a comment |
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1 Answer
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active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
It's a default implementation of a function. It's so simple that its signature looks almost the same as implementation itself; its signature is Throwable => Unit, and it is implemented with the trivial body (_: Throwable) => Unit. It means "take some Throwable at input and just don't return anything".
It's the same as implementing it as (a: Throwable) => Unit, but then compiler would complain that a is unused.
Another alternative for the same thing is (a: Throwable) => ().
answered Jan 2 at 17:42
sloucslouc
5,7542829
add a comment |
It's a default implementation of a function. It's so simple that its signature looks almost the same as implementation itself; its signature is Throwable => Unit, and it is implemented with the trivial body (_: Throwable) => Unit. It means "take some Throwable at input and just don't return anything".
It's the same as implementing it as (a: Throwable) => Unit, but then compiler would complain that a is unused.
Another alternative for the same thing is (a: Throwable) => ().
answered Jan 2 at 17:42
sloucslouc
5,7542829
add a comment |
It's a default implementation of a function. It's so simple that its signature looks almost the same as implementation itself; its signature is Throwable => Unit, and it is implemented with the trivial body (_: Throwable) => Unit. It means "take some Throwable at input and just don't return anything".
It's the same as implementing it as (a: Throwable) => Unit, but then compiler would complain that a is unused.
Another alternative for the same thing is (a: Throwable) => ().
answered Jan 2 at 17:42
sloucslouc
5,7542829
It's a default implementation of a function. It's so simple that its signature looks almost the same as implementation itself; its signature is Throwable => Unit, and it is implemented with the trivial body (_: Throwable) => Unit. It means "take some Throwable at input and just don't return anything".
It's the same as implementing it as (a: Throwable) => Unit, but then compiler would complain that a is unused.
Another alternative for the same thing is (a: Throwable) => ().
answered Jan 2 at 17:42
sloucslouc
5,7542829
edited Jan 2 at 17:56
answered Jan 2 at 17:42
sloucslouc
5,7542829
answered Jan 2 at 17:42
sloucslouc
5,7542829
answered Jan 2 at 17:42
sloucslouc
5,7542829
5,7542829
add a comment |
add a comment |
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2
_means anything. In this case in particular the idea is, given any parameter just ignore it. And the body of the function just returns Unit - in other words the default is an empty callback that does nothing rewarding of the value passed to the callback function.– Luis Miguel Mejía Suárez
Jan 2 at 17:42