[BUG] "cast from Nil to Crystal::GenericInstanceType+ "

[TachoMex]

Hello, I found a bug while solving this

Here are some details:

cast from Nil to Crystal::GenericInstanceType+ failed, at /crystal/src/compiler/crystal/types.cr:1543:20:1543 (TypeCastError)
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Error: you've found a bug in the Crystal compiler. Please open an issue, including source code that will allow us to reproduce the bug: https://github.com/crystal-lang/crystal/issues
$ crystal -v
Crystal 0.25.1 [b782738ff] (2018-06-27)

LLVM: 4.0.0
Default target: x86_64-unknown-linux-gnu

$ uname -a
Linux ubuntu 4.15.0-23-generic #25-Ubuntu SMP Wed May 23 18:02:16 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

The source is:

# @matrix = File.read_lines("../081.in")
#              .map do |row|
#                row.split(',').map { |x| x.to_i }
#              end
matrix = [
  [131, 673, 234, 103, 18],
  [201, 96, 342, 965, 150],
  [630, 803, 746, 422, 111],
  [537, 699, 497, 121, 956],
  [805, 732, 524, 37, 331]
]

class P082
  Steps = [{ 1, 0 }, { -1, 0 }, { 0, 1 }]

  getter :best

  def initialize(matrix)
    @best = 10**9
    @n = matrix.size
    @matrix = matrix
    @visited = Array.new(N) { Array.new(N, false) }
  end

  def find(i, j, current)
    return if current > @best
    if j == @n - 1
      @best = [current, @best].min
      return
    end
    @visited[i][j] = true
    current += @matrix[i][j]
    Steps.each do |di, dj|
      new_i = di + i
      new_j = dj + j
      next if new_i < 0 || new_i >= @n
      next if new_j < 0 || new_j >= @n
      next if @visited[new_i][new_j]
      find(new_i, new_j, @visited, current)
    end

    current -= @matrix[i][j]
    @visited[i][j] = false
  end

  def solve
    (0...@n).each do |i|
      find(i, 0, 0)
    end
  end
end

solution = P082.new(matrix)
solution.solve
puts solution.best

I'm happy of helping at least with a bug reported.
If I can help don't hesitate on contact me.

Thanks guys and keep up the good job!

[asterite]

Reduced:

class Foo
  def initialize
    @x = Array.new(10) { Array.new(10, false) }
  end
end

Foo.new

[Daniel-Worrall]

Minimal code is

class Foo
  def initialize
    @x= Array.new(1) { }
  end
end

Foo.new

It seems it fails due to it being an instance assign as, without it, it compiles as normal.

If N was still there, it would compile complaining about not inferring N.

E: Astersniped

[asterite]

Reduced with --prelude=empty:

class Gen(T)
  def self.new(&block)
    Gen(T).build
  end

  def self.build : self
  end
end

class Foo
  def initialize
    @x = Gen.new { }
  end
end

Foo.new

You can workaround it by manually specifying the type of the instance variables:

class P082
  @visited : Array(Array(...))
  # etc.
end

[Daniel-Worrall]

In fact, this was addressed in #5383 (comment) but perhaps the merged fix addressed the title code and did not aim to solve the code in the comments which was why it was reopened.

[asterite]

I think it's a slightly different scenario.

In any case you'll need to write those type declarations even after the bug is fixed.

Out of curiosity, what are the other 81 problems? :-)

[Daniel-Worrall]

This comment specifically is the reduction that fails in this issue. #5383 (comment)

[TachoMex]

I'm uploading them soon 😛 as starting a polyglot path and my first step is "Solve the first 100".
I'm very happy using crystal. I hope I can contribute to the shards stack soon, but first I have to code a little more.

I have done that as the work around.

[icy-arctic-fox]

Just encountered this with the following code:

class Example
  def initialize(@args = ARGV)
  end
end

https://play.crystal-lang.org/#/r/5s9l

cast from Nil to Crystal::GenericInstanceType+ failed, at /crystal/src/compiler/crystal/types.cr:1632:20:1632 (TypeCastError)

I think it's related to this issue because it's failing to figure out the type is Array(String) from ARGV.
A workaround is to use the following (explicitly defined types):

class Example
  def initialize(@args : Array(String) = ARGV)
  end
end

Not as elegant, but it works.