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Diffstat (limited to 'system/doc/reference_manual/records.xml')
| -rw-r--r-- | system/doc/reference_manual/records.xml | 66 |
1 files changed, 35 insertions, 31 deletions
diff --git a/system/doc/reference_manual/records.xml b/system/doc/reference_manual/records.xml index 04766531df..3294255af9 100644 --- a/system/doc/reference_manual/records.xml +++ b/system/doc/reference_manual/records.xml @@ -32,16 +32,19 @@ elements. It has named fields and is similar to a struct in C. Record expressions are translated to tuple expressions during compilation. Therefore, record expressions are not understood by - the shell unless special actions are taken. See <c>shell(3)</c> - for details.</p> - <p>More record examples can be found in <em>Programming Examples</em>.</p> + the shell unless special actions are taken. For details, see the + <seealso marker="stdlib:shell">shell(3)</seealso> + manual page in STDLIB.</p> + <p>More examples are provided in + <seealso marker="doc/programming_examples"> + Programming Examples</seealso>.</p> <section> <title>Defining Records</title> <p>A record definition consists of the name of the record, followed by the field names of the record. Record and field names must be atoms. Each field can be given an optional default value. - If no default value is supplied, <c>undefined</c> will be used.</p> + If no default value is supplied, <c>undefined</c> is used.</p> <pre> -record(Name, {Field1 [= Value1], ... @@ -60,17 +63,18 @@ the corresponding expression <c>ExprI</c>:</p> <pre> #Name{Field1=Expr1,...,FieldK=ExprK}</pre> - <p>The fields may be in any order, not necessarily the same order as + <p>The fields can be in any order, not necessarily the same order as in the record definition, and fields can be omitted. Omitted - fields will get their respective default value instead.</p> - <p>If several fields should be assigned the same value, + fields get their respective default value instead.</p> + <p>If several fields are to be assigned the same value, the following construction can be used:</p> <pre> #Name{Field1=Expr1,...,FieldK=ExprK, _=ExprL}</pre> - <p>Omitted fields will then get the value of evaluating <c>ExprL</c> + <p>Omitted fields then get the value of evaluating <c>ExprL</c> instead of their default values. This feature was added in Erlang 5.1/OTP R8 and is primarily intended to be used to create - patterns for ETS and Mnesia match functions. Example:</p> + patterns for ETS and Mnesia match functions.</p> + <p><em>Example:</em></p> <pre> -record(person, {name, phone, address}). @@ -84,13 +88,13 @@ lookup(Name, Tab) -> <title>Accessing Record Fields</title> <pre> Expr#Name.Field</pre> - <p>Returns the value of the specified field. <c>Expr</c> should + <p>Returns the value of the specified field. <c>Expr</c> is to evaluate to a <c>Name</c> record.</p> <p>The following expression returns the position of the specified field in the tuple representation of the record:</p> <pre> #Name.Field</pre> - <p>Example:</p> + <p><em>Example:</em></p> <pre> -record(person, {name, phone, address}). @@ -104,8 +108,8 @@ lookup(Name, List) -> <title>Updating Records</title> <pre> Expr#Name{Field1=Expr1,...,FieldK=ExprK}</pre> - <p><c>Expr</c> should evaluate to a <c>Name</c> record. Returns a - copy of this record, with the value of each specified field + <p><c>Expr</c> is to evaluate to a <c>Name</c> record. A + copy of this record is returned, with the value of each specified field <c>FieldI</c> changed to the value of evaluating the corresponding expression <c>ExprI</c>. All other fields retain their old values.</p> @@ -116,17 +120,17 @@ Expr#Name{Field1=Expr1,...,FieldK=ExprK}</pre> <title>Records in Guards</title> <p>Since record expressions are expanded to tuple expressions, creating records and accessing record fields are allowed in - guards. However all subexpressions, for example for field - initiations, must of course be valid guard expressions as well. - Examples:</p> + guards. However all subexpressions, for example, for field + initiations, must be valid guard expressions as well.</p> + <p><em>Examples:</em></p> <code type="none"> handle(Msg, State) when Msg==#msg{to=void, no=3} -> ... handle(Msg, State) when State#state.running==true -> ...</code> - <p>There is also a type test BIF <c>is_record(Term, RecordTag)</c>. - Example:</p> + <p>There is also a type test BIF <c>is_record(Term, RecordTag)</c>.</p> + <p><em>Example:</em></p> <pre> is_person(P) when is_record(P, person) -> true; @@ -136,18 +140,18 @@ is_person(_P) -> <section> <title>Records in Patterns</title> - <p>A pattern that will match a certain record is created the same + <p>A pattern that matches a certain record is created in the same way as a record is created:</p> <pre> #Name{Field1=Expr1,...,FieldK=ExprK}</pre> - <p>In this case, one or more of <c>Expr1</c>...<c>ExprK</c> may be + <p>In this case, one or more of <c>Expr1</c>...<c>ExprK</c> can be unbound variables.</p> </section> <section> - <title>Nested records</title> - <p>Beginning with R14 parentheses when accessing or updating nested - records can be omitted. Assuming we have the following record + <title>Nested Records</title> + <p>Beginning with Erlang/OTP R14, parentheses when accessing or updating nested + records can be omitted. Assume the following record definitions:</p> <pre> -record(nrec0, {name = "nested0"}). @@ -156,12 +160,12 @@ is_person(_P) -> N2 = #nrec2{}, </pre> - <p>Before R14 you would have needed to use parentheses as following:</p> + <p>Before R14, parentheses were needed as follows:</p> <pre> "nested0" = ((N2#nrec2.nrec1)#nrec1.nrec0)#nrec0.name, N0n = ((N2#nrec2.nrec1)#nrec1.nrec0)#nrec0{name = "nested0a"}, </pre> - <p>Since R14 you can also write:</p> + <p>Since R14, the following can also be written:</p> <pre> "nested0" = N2#nrec2.nrec1#nrec1.nrec0#nrec0.name, N0n = N2#nrec2.nrec1#nrec1.nrec0#nrec0{name = "nested0a"},</pre> @@ -170,23 +174,23 @@ N0n = N2#nrec2.nrec1#nrec1.nrec0#nrec0{name = "nested0a"},</pre> <section> <title>Internal Representation of Records</title> <p>Record expressions are translated to tuple expressions during - compilation. A record defined as</p> + compilation. A record defined as:</p> <pre> -record(Name, {Field1,...,FieldN}).</pre> - <p>is internally represented by the tuple</p> + <p>is internally represented by the tuple:</p> <pre> {Name,Value1,...,ValueN}</pre> - <p>where each <c>ValueI</c> is the default value for <c>FieldI</c>.</p> + <p>Here each <c>ValueI</c> is the default value for <c>FieldI</c>.</p> <p>To each module using records, a pseudo function is added during compilation to obtain information about records:</p> <pre> record_info(fields, Record) -> [Field] record_info(size, Record) -> Size</pre> - <p><c>Size</c> is the size of the tuple representation, that is + <p><c>Size</c> is the size of the tuple representation, that is, one more than the number of fields.</p> <p>In addition, <c>#Record.Name</c> returns the index in the tuple - representation of <c>Name</c> of the record <c>Record</c>. - <c>Name</c> must be an atom.</p> + representation of <c>Name</c> of the record <c>Record</c>.</p> + <p><c>Name</c> must be an atom.</p> </section> </chapter> |