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Throws an error if the value is false or nil, otherwise returns all its arguments, like assert.

The message can be:

• nil, which throws "assertion failed!";
• a string, formatted with the remaining arguments when there are any;
• an Error, which is thrown as is;
• an error class, created with the string formatted from the remaining arguments.

local file = assert( open( path ), "cannot open '%s'", path )
assert( size >= 0, ValueError, "size must be positive, got %d", size )

Throws an error with the specified message and level.

An Error that already has a call stack is rethrown as is; if it was captured in another thread (e.g. inside a resumed coroutine) the frames leading here are added below it. Call Error:reset before throwing the same object again to capture a fresh stack.

Values that are neither errors nor strings (signals like ACTION_CANCEL) are thrown as is inside protected calls and coroutines, so they keep their identity.

Returns the metatable of the given value, or nil if it doesn't have one.

Unlike the standard getmetatable, this ignores the __metatable field, so it can reach metatables that are protected from normal code.

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Returns the value of the key in a table.

Returns three values (an iterator function, the table t, and 0) so that the construction

    for i,v in ipairs(t) do body end

will iterate over the key–value pairs (1,t[1]), (2,t[2]), ..., up to the first absent index.

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Returns the length of the object value, without invoking the __len metamethod.

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If t has a metamethod __pairs, calls it with t as argument and returns the first three results from the call.

Otherwise, returns three values: the next function, the table t, and nil, so that the construction

    for k,v in pairs(t) do body end

will iterate over all key–value pairs of table t.

See function next for the caveats of modifying the table during its traversal.

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Prints the given arguments to the console.

If e has a metamethod __tonumber, calls it with e and base as arguments and returns its result.

When called with no base, tonumber tries to convert its argument to a number. If the argument is already a number or a string convertible to a number, then tonumber returns this number; otherwise, it returns fail.

The conversion of strings can result in integers or floats, according to the lexical conventions of Lua (see §3.1). The string may have leading and trailing spaces and a sign.

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Receives a value of any type and converts it to a string in a human-readable format.

If the metatable of v has a __tostring field, then tostring calls the corresponding value with v as argument, and uses the result of the call as its result.

Otherwise, if the metatable of v has a __name field with a string value, tostring may use that string in its final result.

For complete control of how numbers are converted, use string.format.

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