NAME
	type_field - bit field used for optimizations

DESCRIPTION
	Type fields are used by arrays, mappings and some svalue operations
	for optimization. The type field consists of OR:ed bits, one for
	each type. The bit for an array is 1<<T_ARRAY (same as BIT_ARRAY)
	The bit for a string is 1<<T_STRING (or BIT_STRING) etc.

	A bit field never has to be exact, it needs to have at least those
	bits that are present in the operation. It is never harmful to have
	too many bits though. It seldom pays off to calculate the bit field
	explicitly, so if you don't know what types are involved you should
	use -1 for the type field.

KEYWORDS
	data_types

SEE ALSO
	mapping, array, svalue
