18.3 String Construction

LispWorks default string construction is affected by the value of lw:*default-character-element-type* . If the value is base-char then:

returns a simple-base-string . If the value is lw:simple-char then the same form returns a lw:simple-text-string .

This variable merely provides the default behaviour. If enough information is supplied, then a string of suitable type is constructed. For instance, the form:

constructs a string of a type that can hold its elements, regardless of the value of lw:*default-character-element-type* .

Other string constructors also take their default from this variable. For instance, the string reader will always construct a string of type determined by this variable, unless it sees a character of a larger type, in which case a suitable string is constructed.

The initial value of lw:*default-character-element-type* is base-char, to avoid programs that only require 8-bit strings needlessly creating larger string objects. If your application uses Unicode characters beyond the Latin-1 range (characters of type extended-char ) then you should consider which of the following two approaches to use:

• Ensure that all strings which may hold extended-char s are constructed explicitly with the appropriate type. This is the conservative approach, allowing you to avoid allocation of 16-bit strings where these are not required. Note that you can use the specialised accessors such as lw:stchar for strings of type lw:simple-text-string .
• Change the default so that by default 16-bit strings are allocated. Do this by:
  (set-default-character-element-type 'lw:simple-char)
Bear in mind that this is a global setting which affects default string construction for the entire system. It could be called from a user interface, depending on whether the user needs to handle extended-char s.
  Note: Do not attempt to bind or set lw:*default-character-element-type*.