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| author | Doug Rohrer <[email protected]> | 2016-10-04 17:10:40 -0400 |
|---|---|---|
| committer | GitHub <[email protected]> | 2016-10-04 17:10:40 -0400 |
| commit | 33296501241d80df3dec8ee422bf8743558258af (patch) | |
| tree | 3f2ef88c2f0f67d9333a8ea05805a131f3c28c74 /system/doc/reference_manual | |
| parent | 634d26929bb5852958870a7b18f67b4b8702bfa2 (diff) | |
| download | otp-33296501241d80df3dec8ee422bf8743558258af.tar.gz otp-33296501241d80df3dec8ee422bf8743558258af.tar.bz2 otp-33296501241d80df3dec8ee422bf8743558258af.zip | |
Fix reference to automatic `undefined` field declared types.
In 8ce35b287fb50a6845fccf6a13c672aae303dc91 automatic insertion of `undefined` for record fields without initializers was removed, but this was not noted in the documentation. Add a warning about this change using similar verbiage as the original docs.
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: |