diff options
Diffstat (limited to 'system/doc/reference_manual')
| -rw-r--r-- | system/doc/reference_manual/typespec.xml | 15 |
1 files changed, 9 insertions, 6 deletions
diff --git a/system/doc/reference_manual/typespec.xml b/system/doc/reference_manual/typespec.xml index 1899efd5f3..4421529dda 100644 --- a/system/doc/reference_manual/typespec.xml +++ b/system/doc/reference_manual/typespec.xml @@ -409,11 +409,13 @@ The initial values for fields are to be compatible with (that is, a member of) the corresponding types. This is checked by the compiler and results in a compilation error - if a violation is detected. For fields without initial values, - the singleton type <c>'undefined'</c> is added to all declared types. - In other words, the following two record declarations have identical - effects: + if a violation is detected. </p> + <warning> + <p>In previous (pre-19) versions of Erlang, for fields without initial values, + the singleton type <c>'undefined'</c> was added to all declared types. + In other words, the following two record declarations had identical + effects:</p> <pre> -record(rec, {f1 = 42 :: integer(), f2 :: float(), @@ -423,9 +425,10 @@ f2 :: 'undefined' | float(), f3 :: 'undefined' | 'a' | 'b'}).</pre> <p> - For this reason, it is recommended that records contain initializers, - whenever possible. + This is no longer the case. If you require <c>'undefined'</c> in your record field + type, you must explicitly add it to the typespec, as in the 2nd example. </p> + </warning> <p> Any record, containing type information or not, once defined, can be used as a type using the following syntax: |