Re: [Vala] help with java to vala



On Thu, 2012-10-25 at 13:00 -0700, bsquared wrote:
I attempted a simple test using this:
8< ------------------------------------------------
      private static const Set<string> STATIC_SET;
      static construct {
              STATIC_SET = new HashSet<string> ();
              STATIC_SET.add ("Hello");
              STATIC_SET.add ("World");
      }
------------------------------------------------ >8

with this result:
8< ------------------------------------------------
valac --pkg gee-1.0 hello_set.vala
hello_set.vala:5.4-5.47: error: `Gee.Set<string>' not supported as type
for constants
      private static const Set<string> STATIC_SET;
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
hello_set.vala:8.3-8.16: error: The name `add' does not exist in the
context of `HelloTest.STATIC_SET'
              STATIC_SET.add("Hello");
              ^^^^^^^^^^^^^^
hello_set.vala:9.3-9.16: error: The name `add' does not exist in the
context of `HelloTest.STATIC_SET'
              STATIC_SET.add("World");
              ^^^^^^^^^^^^^^
Compilation failed: 3 error(s), 0 warning(s)
------------------------------------------------ >8


To my untrained eye this appears to indicate that I cannot use these as
constants.  If I drop 'const' from the declaration it compiles and runs
correctly.

This is the expected result - if the Set is constant, then you can't
call the add method on it. It looks like the Gee Set type simply doesn't
support being used as a constant.

I think that the only types that you can actually use as constants in
Vala are ones that compile to basic/simple C types, and therefore could
be created using constant C initializers. If you have to write data to
the object at run-time to fill it, it's not a compile-time constant,
after all.

This limits you to using things like arrays of structures, for example.

If you really want a run-time initialized Set, then it will have to be
non-const.

-- 
Calvin Walton <calvin walton kepstin ca>

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