However, it's possible to circumvent this restriction by having implicits take implicit parameters.Įlaborating on the argument, beyond the more subjective argument around the difference between the apparent explicit meaning of the program and the actual meaning after applying the conversions (one could just as easily argue (and (implicitly.) nearly every other language designer does by not having Scala-style conversions) that trying any implicit conversions unduly increases the difference between what is written and what the program actually does), consider the consequence of having no limit on the conversion depth (recall the dictum: "zero, one, or no limit") For sanity's sake, the compiler does not insert further implicit conversions when it's in the middle of trying another implicit conversion. Doing so would cause compile times to increase dramatically on erroneous code, and it would increase the difference between what the programmer writes and what the program actually does. The compiler will never rewrite x + y to convert1(convert2(x)) + y. One at a time rule: Only one implicit is inserted. Odersky, Spoon, and Venners Programming in Scala (I'm quoting Third Edition, using Scala 2 terminology, but modulo the terminology difference it still applies): The limitation is a consciously chosen one. It's not a question of "can't" but "doesn't". To compiler can now chain conversions: val t3: T3 = t1 //OKīonus point: this new generic conversion can even recursively call itself, meaning that we can chain infinite conversions. Override def apply(x: A): C = conv2.apply(conv1.apply(x))
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My Workaround: it turns out that we can implicitly tell to compiler how to chain conversions by defining a generic conversion from A to C, given that we know how to convert A to B and B to C: given (using conv1: Conversion)(using conv2: Conversion): Conversion with My Question: is there a specific reason why the compiler cannot natively (see workaround) chain conversions ?
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The following code then compiles fine: type T1īut what happens when we try to go from T1 to T3 ? The compiler won't let us: val t3: T3 = t1 We also define two given instances of the Conversion class so that the compiler can go from T1 to T2 and from T2 to T3. Following is a sample Scala program which takes name as input and prints hello message with your name.Let T1, T2, T3 be three types. OneCompiler's Scala online editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. The editor shows sample boilerplate code when you choose language as Scala and start coding.
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