Ruby の StandardError でどういう間違いをすると, どの例外が発生するのかのメモ

'1'.to_i(1, 2) rescue $!
  # => #<ArgumentError: wrong number of arguments (given 2, expected 0..1)>

'1'.to_i 1 rescue $! # => #<ArgumentError: invalid radix 1>

catch(1) { throw 2 } rescue $! # => #<UncaughtThrowError: uncaught throw 2>

'hello'.encode 'CUSTOM_ENCODING' rescue $!
  # => #<Encoding::ConverterNotFoundError: code converter not found (UTF-8 to CUSTOM_ENCODING)>

fiber = Fiber.new {}
fiber.resume
fiber.resume rescue $! # => #<FiberError: dead fiber called>

File.open('example.txt') do |f|
  f.write('Hello World') rescue $! # => #<IOError: not opened for writing>
end

File.open('example.txt') do |f|
  f.close
  f.read rescue $! # => #<IOError: closed stream>
end

File.open('example.txt') do |f|
  f.read
  f.readline rescue $! # => #<EOFError: end of file reached>
end

[:a].fetch 1 rescue $!
  # => #<IndexError: index 1 outside of array bounds: -1...1>

{a: :a}.fetch :b rescue $! # => #<KeyError: key not found: :b>

enum = [:a].each
enum.next
enum.next rescue $! # => #<StopIteration: iteration reached an end>

def foo; yield end
foo rescue $! # => #<LocalJumpError: no block given (yield)>

def bar; proc { return } end
bar.call rescue $! # => #<LocalJumpError: unexpected return>

foo rescue $!
  # => #<NameError: undefined local variable or method `foo' for main:Object>

Symbol.const_set :a, :a rescue $! # => #<NameError: wrong constant name a>

Symbol::A rescue $! # => #<NameError: uninitialized constant Symbol::A>

'hello'.pascalcase rescue $!
  # => #<NoMethodError: undefined method `pascalcase' for "hello":String>

[:a, :b].drop 1_000**10 rescue $!
  # => #<RangeError: bignum too big to convert into `long'>

Float::INFINITY.to_i rescue $! # => #<FloatDomainError: Infinity>
Float::INFINITY.to_r rescue $! # => #<FloatDomainError: Infinity>
Float::NAN.to_i rescue $!      # => #<FloatDomainError: NaN>
Float::NAN.to_r rescue $!      # => #<FloatDomainError: NaN>

Regexp.new '+' rescue $!
  # => #<RegexpError: target of repeat operator is not specified: /+/>
Regexp.new '*' rescue $!
  # => #<RegexpError: target of repeat operator is not specified: /*/>
Regexp.new '?' rescue $!
  # => #<RegexpError: target of repeat operator is not specified: /?/>
Regexp.new '\1' rescue $!
  # => #<RegexpError: invalid backref number/name: /\1/>
Regexp.new '\k<a>' rescue $!
  # => #<RegexpError: undefined name <a> reference: /\k<a>/>
Regexp.new '\g<a>' rescue $!
  # => #<RegexpError: undefined name <a> reference: /\g<a>/>

raise 'a generic error' rescue $! # => #<RuntimeError: a generic error>

[].freeze << :a rescue $! # => #<FrozenError: can't modify frozen Array>
{}.freeze.merge!({a: :a}) rescue $! # => #<FrozenError: can't modify frozen Hash>

File.open('example.txt') rescue $!
  # => #<Errno::ENOENT: No such file or directory @ rb_sysopen - example.txt>

File.open('example.txt', 'w') rescue $!
  # => #<Errno::EACCES: Permission denied @ rb_sysopen - example.txt>

Thread.new rescue $! # => #<ThreadError: must be called with a block>

1 + '1' rescue $! # => #<TypeError: String can't be coerced into Integer>

'1' + 1 rescue $!
  # => #<TypeError: no implicit conversion of Integer into String>

'Hello' + :World rescue $!
  # => #<TypeError: no implicit conversion of Symbol into String>

[:a, :b].fetch '0' rescue $!
  # => #<TypeError: no implicit conversion of String into Integer>

1 / 0 rescue $!    # => #<ZeroDivisionError: divided by 0>
1/1r / 0 rescue $! # => #<ZeroDivisionError: divided by 0>