Exception naming conventions: rely on module name?

[Edwin Fine]

I am wondering about design alternatives regarding exception naming in
Ruby. Is there a naming convention for exceptions that are declared
inside a module?

For example, let's say we have a module named MP3, and we want to have a
base exception for MP3-related errors. There are two basic choices I am
considering here:

module MP3
class MP3Error < StandardError; end # Alternative 1
class Error < StandardError; end # Alternative 2
end

Outside the module, Error would be disambiguated by MP3 (MP3::Error).
However, I am uneasy about this, because of the following situation.
Imagine someone has some existing code that mixes in module Other:

module Other
class Error < StandardError; end
end

class Foo
include Other
def Foo.oops
raise Error, "Who am I?"
rescue Error => e
puts "#{e} #{e.class.name}"
end
end

Foo.oops # Who am I? Other::Error

Now this hapless person mixes in MP3.

class Foo
include Other
include MP3
def Foo.oops
raise Error, "Who am I?"
rescue Error => e
puts "#{e} #{e.class.name}"
end
end

Foo.oops # Who am I? MP3::Error

- Is this a real concern?
- Do you think it would be better to have exception names that are less
likely to clash at the cost of some duplication (e.g. MP3::MP3Error
instead of MP3::Error)?

 

[Eric Hodel]

I am wondering about design alternatives regarding exception naming in
Ruby. Is there a naming convention for exceptions that are declared
inside a module?

For example, let's say we have a module named MP3, and we want to
have a base exception for MP3-related errors. There are two basic
choices I am considering here:

module MP3
class MP3Error < StandardError; end # Alternative 1
class Error < StandardError; end # Alternative 2
end

I typically use #2

Outside the module, Error would be disambiguated by MP3 (MP3::Error).
However, I am uneasy about this, because of the following situation.
Imagine someone has some existing code that mixes in module Other:

module Other
class Error < StandardError; end
end

class Foo
include Other
def Foo.oops
raise Error, "Who am I?"
rescue Error => e
puts "#{e} #{e.class.name}"
end
end

Foo.oops # Who am I? Other::Error

Always fully qualify.

Now this hapless person mixes in MP3.

class Foo
include Other
include MP3
def Foo.oops
raise Error, "Who am I?"
rescue Error => e
puts "#{e} #{e.class.name}"
end
end

Foo.oops # Who am I? MP3::Error

- Is this a real concern?

No. Fully qualify and it won't be a problem.

- Do you think it would be better to have exception names that are
less likely to clash at the cost of some duplication (e.g.
MP3::MP3Error instead of MP3::Error)?

MP3::MP3Error is redundant. There is no problem if you raise
MP3::Error instead. If a consumer of your library decides to omit
Error that's their bug, not yours.

 

[Guest]

MP3::MP3Error is redundant. There is no problem if you raise
MP3::Error instead. If a consumer of your library decides to omit
Error that's their bug, not yours.

Thank you for your advice. I will follow it.
Ed