Stable Identifier in Regex pattern match via implicit conversion
This works...
val re = "a.c".r
"abc" match {
case re() => "HIT"
case _ => "miss"
}
//res0: String = HIT
...because the Regex class, and thus every Regex instance, has an unapplySeq() method that gets invoked when pattern matching.
But it only works if the Regex variable, re in this case, is a val. If it's a var or def then it won't compile, Error: not found: value re. This is because, I believe, the LHS of a pattern match is required to be a Stable Identifier, and vars/defs don't qualify.
This also works...
implicit class RE(sc :StringContext) {
def re = "a.c".r
}
"abc" match {
case re"" => "HIT"
case _ => "miss"
}
//res1: String = HIT
...because of the following transformations:
re""creates aStringContextinstance- an instance of class
REis created through implicit conversion - the member
re, of typeRegex, is accessed
unapplySeq()is invoked, and pattern matching proceeds as before
Notice that, in this case, the re variable does not have to be a val. It makes no difference whether it's a val, var, or def. Notice also that re"" is not a stand-alone construct. It won't compile outside of this pattern-matching context.
So, if all this is reasonably accurate, the question is: Where is the stable identifier? At what point was that achieved?
scala pattern-matching implicit-conversion
asked Jan 3 at 5:34
jwvhjwvh
28k52141
add a comment |
This works...
val re = "a.c".r
"abc" match {
case re() => "HIT"
case _ => "miss"
}
//res0: String = HIT
...because the Regex class, and thus every Regex instance, has an unapplySeq() method that gets invoked when pattern matching.
But it only works if the Regex variable, re in this case, is a val. If it's a var or def then it won't compile, Error: not found: value re. This is because, I believe, the LHS of a pattern match is required to be a Stable Identifier, and vars/defs don't qualify.
This also works...
implicit class RE(sc :StringContext) {
def re = "a.c".r
}
"abc" match {
case re"" => "HIT"
case _ => "miss"
}
//res1: String = HIT
...because of the following transformations:
re""creates aStringContextinstance- an instance of class
REis created through implicit conversion - the member
re, of typeRegex, is accessed
unapplySeq()is invoked, and pattern matching proceeds as before
Notice that, in this case, the re variable does not have to be a val. It makes no difference whether it's a val, var, or def. Notice also that re"" is not a stand-alone construct. It won't compile outside of this pattern-matching context.
So, if all this is reasonably accurate, the question is: Where is the stable identifier? At what point was that achieved?
scala pattern-matching implicit-conversion
asked Jan 3 at 5:34
jwvhjwvh
28k52141
add a comment |
This works...
val re = "a.c".r
"abc" match {
case re() => "HIT"
case _ => "miss"
}
//res0: String = HIT
...because the Regex class, and thus every Regex instance, has an unapplySeq() method that gets invoked when pattern matching.
But it only works if the Regex variable, re in this case, is a val. If it's a var or def then it won't compile, Error: not found: value re. This is because, I believe, the LHS of a pattern match is required to be a Stable Identifier, and vars/defs don't qualify.
This also works...
implicit class RE(sc :StringContext) {
def re = "a.c".r
}
"abc" match {
case re"" => "HIT"
case _ => "miss"
}
//res1: String = HIT
...because of the following transformations:
re""creates aStringContextinstance- an instance of class
REis created through implicit conversion - the member
re, of typeRegex, is accessed
unapplySeq()is invoked, and pattern matching proceeds as before
Notice that, in this case, the re variable does not have to be a val. It makes no difference whether it's a val, var, or def. Notice also that re"" is not a stand-alone construct. It won't compile outside of this pattern-matching context.
So, if all this is reasonably accurate, the question is: Where is the stable identifier? At what point was that achieved?
scala pattern-matching implicit-conversion
asked Jan 3 at 5:34
jwvhjwvh
28k52141
This works...
val re = "a.c".r
"abc" match {
case re() => "HIT"
case _ => "miss"
}
//res0: String = HIT
...because the Regex class, and thus every Regex instance, has an unapplySeq() method that gets invoked when pattern matching.
But it only works if the Regex variable, re in this case, is a val. If it's a var or def then it won't compile, Error: not found: value re. This is because, I believe, the LHS of a pattern match is required to be a Stable Identifier, and vars/defs don't qualify.
This also works...
implicit class RE(sc :StringContext) {
def re = "a.c".r
}
"abc" match {
case re"" => "HIT"
case _ => "miss"
}
//res1: String = HIT
...because of the following transformations:
re""creates aStringContextinstance- an instance of class
REis created through implicit conversion - the member
re, of typeRegex, is accessed
unapplySeq()is invoked, and pattern matching proceeds as before
Notice that, in this case, the re variable does not have to be a val. It makes no difference whether it's a val, var, or def. Notice also that re"" is not a stand-alone construct. It won't compile outside of this pattern-matching context.
So, if all this is reasonably accurate, the question is: Where is the stable identifier? At what point was that achieved?
scala pattern-matching implicit-conversion
scala pattern-matching implicit-conversion
asked Jan 3 at 5:34
jwvhjwvh
28k52141
asked Jan 3 at 5:34
jwvhjwvh
28k52141
edited Jan 3 at 5:40
jwvh
asked Jan 3 at 5:34
jwvhjwvh
28k52141
asked Jan 3 at 5:34
jwvhjwvh
28k52141
asked Jan 3 at 5:34
jwvhjwvh
28k52141
28k52141
add a comment |
add a comment |
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