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103 строки
2.2 KiB
Plaintext
103 строки
2.2 KiB
Plaintext
= Exception Handling
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Exceptions are rescued in a +begin+/+end+ block:
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begin
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# code that might raise
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rescue
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# handle exception
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end
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If you are inside a method, you do not need to use +begin+ or +end+ unless you
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wish to limit the scope of rescued exceptions:
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def my_method
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# ...
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rescue
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# ...
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end
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The same is true for a +class+, +module+, and +block+:
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[0, 1, 2].map do |i|
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10 / i
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rescue ZeroDivisionError
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nil
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end
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#=> [nil, 10, 5]
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You can assign the exception to a local variable by using <tt>=>
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variable_name</tt> at the end of the +rescue+ line:
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begin
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# ...
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rescue => exception
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warn exception.message
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raise # re-raise the current exception
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end
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By default, StandardError and its subclasses are rescued. You can rescue a
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specific set of exception classes (and their subclasses) by listing them after
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+rescue+:
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begin
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# ...
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rescue ArgumentError, NameError
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# handle ArgumentError or NameError
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end
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You may rescue different types of exceptions in different ways:
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begin
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# ...
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rescue ArgumentError
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# handle ArgumentError
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rescue NameError
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# handle NameError
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rescue
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# handle any StandardError
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end
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The exception is matched to the rescue section starting at the top, and matches
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only once. If an ArgumentError is raised in the begin section, it will not be
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handled in the StandardError section.
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You may retry rescued exceptions:
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begin
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# ...
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rescue
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# do something that may change the result of the begin block
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retry
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end
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Execution will resume at the start of the begin block, so be careful not to
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create an infinite loop.
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Inside a rescue block is the only valid location for +retry+, all other uses
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will raise a SyntaxError. If you wish to retry a block iteration use +redo+.
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See {Control Expressions}[rdoc-ref:syntax/control_expressions.rdoc] for
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details.
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To always run some code whether an exception was raised or not, use +ensure+:
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begin
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# ...
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rescue
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# ...
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ensure
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# this always runs
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end
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You may also run some code when an exception is not raised:
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begin
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# ...
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rescue
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# ...
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else
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# this runs only when no exception was raised
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ensure
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# ...
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end
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