Scala String Interpolation

Question

I am new to Scala and have read threads related to String Interpolation.

My requirement is that , I want to find the type of an expression, before actually evaluating the expression. To make it clear:

val tesType = s"${{10 * Math.cos(0)+ 3}.getClass}"

This gives me the return type of the entire expression.

Is it possible to generalise this by replacing the actual expression by a variable containing the expression? Something like:

val expression="10 * Math.cos(0)+ 3"
val tesType = s"${{expression}.getClass}"

Would something like this be possible or I am totally wrong in thinking in this direction?

Thanks

Yes, once iterpolated, I want it to check for functions inside the string and give the result type accordingly.In the above case, double — ssri
– ssri, Commented Oct 30, 2015 at 14:51
String interpolation happens at compile time, nothing interpreted here. Also, I'd use variables as soon as your type gets a bit more complicated. — Reactormonk
– Reactormonk, Commented Oct 30, 2015 at 14:53
@Reactormonk string interpolation in general does not happen at compile time. That would require macros. — 0__
– 0__, Commented Oct 30, 2015 at 14:55
@0__ I think @Reactormonk referred to the fact that s"some $foo" will be replaced by something like StringContext("some ").s(foo) before actual compilation, but by the compiler. — phipsgabler
– phipsgabler, Commented Oct 30, 2015 at 15:26

vvg · Accepted Answer · 2015-10-30 14:54:10Z

2

It's not possible to do with string interpolation. What you actually want to do is to compile scala code in runtime from string (file etc).

For ex twitter Eval library can be used for this purposes: https://eknet.org/main/dev/runtimecompilescala.html

answered Oct 30, 2015 at 14:54

vvg

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Alexey Romanov · Accepted Answer · 2015-10-30 20:15:11Z

0

If you want the expression to be in a string, then see mst's answer (you can also use scala-compiler itself as a library, but its API is harder to use).

If you have an expression as an expression, you can do

import scala.reflect.runtime.universe._
def typeOfExpr[T: TypeTag](t: => T) = typeOf[T]

typeOfExpr(10 * Math.cos(0)+ 3) // returns Double

answered Oct 30, 2015 at 20:15

Alexey Romanov

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