As of scala 2.10, the following interpolation is possible.
val name = "someName"
val interpolated = s"Hello world, my name is $name"
Now it is also possible defining custom string interpolations, as you can see in the scala documentation in the "Advanced usage" section here http://docs.scala-lang.org/overviews/core/string-interpolation.html#advanced_usage
Now then, my question is... is there a way to obtain the original string, before interpolation, including any interpolated variable names, from inside the implicit class that is defining the new interpolation for strings?
In other words, i want to be able to define an interpolation x, in such a way that when i call
x"My interpolated string has a $name"
i can obtain the string exactly as seen above, without replacing the $name part, inside the interpolation.
Edit: on a quick note, the reason i want to do this is because i want to obtain the original string and replace it with another string, an internationalized string, and then replace the variable values. This is the main reason i want to get the original string with no interpolation performed on it.
Thanks in advance.
Since Scala's string interpolation can handle arbitrary expressions within ${} it has to evaluate the arguments before passing them to the formatting function. Thus, direct access to the variable names is not possible by design. As pointed out by Eugene, it is possible to get the name of a plain variable by using macros. I don't think this is a very scalable solution, though. After all, you'll lose the possibility to evaluate arbitrary expressions. What, for instance, will happen in this case:
x"My interpolated string has a ${"Mr. " + name}"
You might be able to extract the variable name by using macros but it might get complicated for arbitrary expressions. My suggestions would be: If the name of your variable should be meaningful within the string interpolation, make it a part of the data structure. For example, you can do the following:
case class NamedValue(variableName: String, value: Any)
val name = NamedValue("name", "Some Name")
x"My interpolated string has a $name"
The objects are passed as Any* to the x. Thus, you now can match for NamedValue within x and you can do specific things depending on the "variable name", which now is part of your data structure. Instead of storing the variable name explicitly you could also exploit a type hierarchy, for instance:
sealed trait InterpolationType
case class InterpolationTypeName(name: String) extends InterpolationType
case class InterpolationTypeDate(date: String) extends InterpolationType
val name = InterpolationTypeName("Someone")
val date = InterpolationTypeDate("2013-02-13")
x"$name is born on $date"
Again, within x you can match for the InterpolationType subtype and handle things according to the type.
It seems that's not possible. String interpolation seems like a compile feature that compiles the example to:
StringContext("My interpolated string has a ").x(name)
As you can see the $name part is already gone. It became really clear for me when I looked at the source code of StringContext: https://github.com/scala/scala/blob/v2.10.0/src/library/scala/StringContext.scala#L1
If you define x as a macro, then you will be able to see the tree of the desugaring produced by the compiler (as shown by #EECOLOR). In that tree, the "name" argument will be seen as Ident(newTermName("name")), so you'll be able to extract a name from there. Be sure to take a look at macro and reflection guides at docs.scala-lang.org to learn how to write macros and work with trees.
Related
I imagine I'm screwing something up with these declarations, but I've got a groovy class with a field defined like this:
Map<String, SomeType> _someField = [:]
I do inserts like this:
_someField.put( someStringVariable, someTypeInstance )
...and then later, when I check whether a key I know has been mapped is present, the check fails:
_someField.containsKey( someStringVariable )
The only way I can get this to succeed is by calling toString(), like so:
_someField.containsKey( someStringVariable.toString() )
I'm using the generic declaration of the map so my IDE gives me auto completion on the value types, so I'd really like (I think) to keep the type information there.
I've tried changing the key type from String to GString, but to no avail. I've tried changing the map initialization from the groovy shorthand [:] to new LinkedHashMap<>, also to no avail.
Any ideas whether I can keep the type information and avoid having to use toString()?
So this was a case where the variable being fed to containsKey() in the instances where it is failing were of type org.codehaus.groovy.runtime.GStringImpl because they were generated by a function that was performing variable expansion on map values, and that function was creating groovy interpolated strings for values instead of Java Strings.
A quick check on the type of the variable confirmed the type problem, and then it was just a matter of tracking back to find the source of the interpolated string.
I have a phrase, where only some words will change, and I need to store those words on a variable.
Example:
phrase = "I cannot connect to server XPTO\TEST for the last five hours"
The only part that will change is XPTO\TEST and I need to store it on a variable so that I can use it later.
Any ideas, or is it possible?
Seems like you need some form of placeholders, if that is a case, then you can use string.format or string.gsub.
local t = {name="lua", version="5.3"}
x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t)
--> x="lua-5.3.tar.gz"
With PHP for example you can achieve what you want without any extra work done, because there is a feature called string interpolation (wiki).
But at the same time Lua doesn't have one, that's why you can't do that without extra string post-processing.
Basically I want to print something in the unit data type via my own structure and signature that requires this to happen as its data type is unit and i want to "show" it.
So I need to "print" it.
I tried the unit.to String function, and tried to convert it to a character first, but to no avail.
print(unit.to String(symex))
-undefined variable or constructor unit.to String
The unit type has only one value, (). That is, the value doesn't contain any information.
Creating a unit to string function is rather simple:
fun unitToString () = "()"
As there is only one possible value, it can have only one possible representation as a string.
However, since the value doesn't actually contain any information, you most likely don't want to operate on the unit value, but rather some other value.
I have a question about the use of string map in TCL.
Is there a way to detect when this function has changed the previous value of the mapped string?
For example, in this case:
set location "default_user: admin"
set new_user "user"
set new_location [string map [list "admin" $new_user] $location]
In this case, I want to know if new_location has a different value than location (without comparing both variables, maybe there is a more elegant way).
My real case is more complicated than this one, I have a variable with the content of a html file, and I want to substitute a specific value for another one or read from another variable if there was no subtitution.
Thanks for your help, I hope everything is clear in the example above.
string map function does not imply a return number of replacements. In order to get the number of substitutions may be used regsub -all function that returns the value. You can also use a string first to value before string map, to learn whether there is a variable line of the desired value.
I have a mathematical expression in string form like:
string strExpression = "10+100+Math.Sin(90)";
I want to simply assign this expression (at run time) to a float variable (say result), so that it becomes the following code statement:
float result = 10+100+Math.Sin(90);
How can I do this?
You have to compile the expression within a syntactically correct code block. See http://devreminder.wordpress.com/net/net-framework-fundamentals/c-dynamic-math-expression-evaluation/ as an example.
Edit: Or alternatively write your own expression parser if the expression is going to be VERY simple (I wouldn't recommend this though)
You could use CS-Script to dynamically make a class with a method that you can run, if you don't want to write your own parser but rather use C# which you allready know..