Elixir v1.6.0 Exception behaviour View Source
Functions to format throw/catch/exit and exceptions.
Note that stacktraces in Elixir are updated on throw,
errors and exits. For example, at any given moment,
System.stacktrace/0 will return the stacktrace for the
last throw/error/exit that occurred in the current process.
Do not rely on the particular format returned by the format*
functions in this module. They may be changed in future releases
in order to better suit Elixir’s tool chain. In other words,
by using the functions in this module it is guaranteed you will
format exceptions as in the current Elixir version being used.
Link to this section Summary
Functions
Attaches information to exceptions for extra debugging
Blames the invocation of the given module, function and arguments
Returns true if the given term is an exception
Normalizes and formats throw/errors/exits and stacktraces
Normalizes and formats any throw/error/exit
Formats an exit. It returns a string
Receives an anonymous function and arity and formats it as shown in stacktraces. The arity may also be a list of arguments
Formats the given file and line as shown in stacktraces.
If any of the values are nil, they are omitted
Receives a module, fun and arity and formats it as shown in stacktraces. The arity may also be a list of arguments
Formats the stacktrace
Receives a stacktrace entry and formats it into a string
Gets the message for an exception
Normalizes an exception, converting Erlang exceptions to Elixir exceptions
Callbacks
Called from Exception.blame/3 to augment the exception struct
Link to this section Types
The kind handled by formatting functions
The exception type
Link to this section Functions
blame(:error, any(), stacktrace()) :: {t(), stacktrace()}
blame(non_error_kind(), payload, stacktrace()) :: {payload, stacktrace()} when payload: var
Attaches information to exceptions for extra debugging.
This operation is potentially expensive, as it reads data from the filesystem, parse beam files, evaluates code and so on.
If the exception module implements the optional blame/2
callbak, it will be invoked to perform the computation.
Blames the invocation of the given module, function and arguments.
This function will retrieve the available clauses from bytecode
and evaluate them against the given arguments. The clauses are
returned as a list of {args, guards} pairs where each argument
and each top-level condition in a guard separated by and/or
is wrapped in a tuple with blame metadata.
This function returns either {:ok, definition, clauses} or :error.
Where definition is :def, :defp, :defmacro or :defmacrop.
Note this functionality requires Erlang/OTP 20, otherwise :error
is always returned.
Returns true if the given term is an exception.
format(kind(), any(), stacktrace() | nil) :: String.t()
Normalizes and formats throw/errors/exits and stacktraces.
It relies on format_banner/3 and format_stacktrace/1
to generate the final format.
Note that {:EXIT, pid} do not generate a stacktrace though
(as they are retrieved as messages without stacktraces).
format_banner(kind(), any(), stacktrace() | nil) :: String.t()
Normalizes and formats any throw/error/exit.
The message is formatted and displayed in the same format as used by Elixir’s CLI.
The third argument, a stacktrace, is optional. If it is
not supplied System.stacktrace/0 will sometimes be used
to get additional information for the kind :error. If
the stacktrace is unknown and System.stacktrace/0 would
not return the stacktrace corresponding to the exception
an empty stacktrace, [], must be used.
Formats an exit. It returns a string.
Often there are errors/exceptions inside exits. Exits are often wrapped by the caller and provide stacktraces too. This function formats exits in a way to nicely show the exit reason, caller and stacktrace.
Receives an anonymous function and arity and formats it as shown in stacktraces. The arity may also be a list of arguments.
Examples
Exception.format_fa(fn -> nil end, 1)
#=> "#Function<...>/1"Formats the given file and line as shown in stacktraces.
If any of the values are nil, they are omitted.
Examples
iex> Exception.format_file_line("foo", 1)
"foo:1:"
iex> Exception.format_file_line("foo", nil)
"foo:"
iex> Exception.format_file_line(nil, nil)
""Receives a module, fun and arity and formats it as shown in stacktraces. The arity may also be a list of arguments.
Examples
iex> Exception.format_mfa Foo, :bar, 1
"Foo.bar/1"
iex> Exception.format_mfa Foo, :bar, []
"Foo.bar()"
iex> Exception.format_mfa nil, :bar, []
"nil.bar()"Anonymous functions are reported as -func/arity-anonfn-count-, where func is the name of the enclosing function. Convert to “anonymous fn in func/arity”
Formats the stacktrace.
A stacktrace must be given as an argument. If not, the stacktrace
is retrieved from Process.info/2.
format_stacktrace_entry(stacktrace_entry()) :: String.t()
Receives a stacktrace entry and formats it into a string.
Gets the message for an exception.
normalize(:error, any(), stacktrace()) :: t()
normalize(non_error_kind(), payload, stacktrace()) :: payload when payload: var
Normalizes an exception, converting Erlang exceptions to Elixir exceptions.
It takes the kind spilled by catch as an argument and
normalizes only :error, returning the untouched payload
for others.
The third argument, a stacktrace, is optional. If it is
not supplied System.stacktrace/0 will sometimes be used
to get additional information for the kind :error. If
the stacktrace is unknown and System.stacktrace/0 would
not return the stacktrace corresponding to the exception
an empty stacktrace, [], must be used.
Link to this section Callbacks
blame(t(), stacktrace()) :: {t(), stacktrace()}
Called from Exception.blame/3 to augment the exception struct.
Can be used to collect additional information about the exception or do some additional expensive computation.