Scala String format named parameters (Winner: Ugliest Code)

Question

I came up with a trick to use named parameters in Scala. Is there a better way? What are the downsides?

<x>
  |CREATE OR REPLACE FUNCTION myFunction({columns.map(column => column.name).
                                          mkString(",\n")})
  |RETURNS BOOLEAN AS $$
  |BEGIN
  | -- more stuff
  |END;
  |$$ LANGUAGE 'plpgsql';
  |</x>.text.stripMargin

Watch out for ampersands in the XML body; they need to be "quoted" as & or placed in braces like {"&"}. Do I win a prize for ugliest code? :-)

@Jean-Philippe Pellet: I need to generate a rather large SQL function in my Scala code, with replacement of parts of the function with calculated pieces (like args above). — Ralph
– Ralph, Commented Apr 28, 2011 at 19:11
I really like your idea! I often had the same problem, not only with SQL. Sometimes one constructs a fat string with format having many many format arguments. — Peter Schmitz
– Peter Schmitz, Commented Apr 28, 2011 at 19:44
@Peter Schmitz: I am also putting Scala code into the inner braces that actually calculates the columns names, etc.: {columns.map(column => column.name).mkString(",\n")} -- see update in the question. — Ralph
– Ralph, Commented Apr 28, 2011 at 20:28

sblundy · Accepted Answer · 2011-04-28 19:22:10Z

2

I think that if you need a string formater on this scale, you need a Builder or a templating engine, like Velocity. Incidentally, I've found Scala's good for builders and DSLs.

answered Apr 28, 2011 at 19:22

sblundy

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2 Comments

mkneissl Over a year ago

I've written a wrapper for velocity two years ago that fits the use case of the question. kneissl.eu/open-source/scala-velocity

Ralph Over a year ago

@mkneissl: Almost gets around the lack of a preprocessor. :-)

Alex Cruise · Accepted Answer · 2011-04-29 00:49:48Z

2

If you don't mind a compiler plugin, try Johannes Rudolph's Scala Enhanced Strings. I like it a lot.

answered Apr 29, 2011 at 0:49

Alex Cruise

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Comments

blast_hardcheese · Accepted Answer · 2013-08-01 13:33:21Z

Good news! Scala 2.10.0 introduced real, functional string interpolation!

The docs are available here: http://docs.scala-lang.org/overviews/core/string-interpolation.html

Here's a quick sample:

In Python, I used to do things like:

print "%(from)s -> %(to)s" % {"from": foo, "to": bar}

now, in Scala 2.10.0+, we can do this!

val from = "Foo"
val to = 256
println(s"$from -> $to")  // Prints: Foo -> 256

There's also some format string support as well, which is pretty awesome:

val from = 10.00  // USD
val to = 984.30  // JPY
println(f"$$$from%.2f -> $to%.2fJPY")  // Prints: $10.00 -> 984.30JPY

Since the second example has some minimal type expressiveness, it also gives us some basic type checking as well!

val from = 10.00
println(f"$$$from%d") // <-- Type error! Found "Double", required "Int"!

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