NAME

       sc::PrefixKeyVal - PrefixKeyVal is a KeyVal that searches a different KeyVal using
       modified keys.

SYNOPSIS

       #include <keyval.h>

       Inherits sc::KeyVal.

   Public Member Functions
       Constructors.
       Construct a PrefixKeyVal, using the given prefix and indices.

           PrefixKeyVal (const Ref< KeyVal > &, int i)
           PrefixKeyVal (const Ref< KeyVal > &, int i, int j)
           PrefixKeyVal (const Ref< KeyVal > &, int i, int j, int k)
           PrefixKeyVal (const Ref< KeyVal > &, int i, int j, int k, int l)
           PrefixKeyVal (const Ref< KeyVal > &, const char *prefix)
           PrefixKeyVal (const Ref< KeyVal > &, const char *prefix, int i)
           PrefixKeyVal (const Ref< KeyVal > &, const char *prefix, int i, int j)
           PrefixKeyVal (const Ref< KeyVal > &, const char *prefix, int i, int j, int k)
           PrefixKeyVal (const Ref< KeyVal > &, const char *prefix, int i, int j, int k, int l)
           ~PrefixKeyVal ()
           void errortrace (std::ostream &fp=ExEnv::err0())
               Write a message to fp describing the error.
           void dump (std::ostream &fp=ExEnv::err0())
               Write a message to fp describing the error.

   Additional Inherited Members

Detailed Description

       PrefixKeyVal is a KeyVal that searches a different KeyVal using modified keys.

       This is convenient for reading keys grouped together with a common prefix. Consider the
       following code:

       sc::Ref<sc::KeyVal> keyval = new sc::PrefixKeyVal('A',original_keyval);
       int r = keyval->intvalue('x');

        This code will assign to r the value associated with 'x' in keyval. keyval will search
       for 'x' by searching for 'A::x' in original_keyval.

       This class is important for implementing constructors that take KeyVal arguments. When an
       object is being constructed from a KeyVal, it may contain another object that must be
       constructed from a KeyVal. In order to let the sub-object read the correct keywords from
       the KeyVal, without knowledge of the containing objects keyword prefix, a PrefixKeyVal can
       be constructed. For example, the code

       class A: public DescribedClass {
          double f0_;
         public:
          A(const Ref<KeyVal> &keyval): f0_(keyval->doublevalue("f0")) {}
       }
       class B: public DescribedClass {
          double f1_;
          Ref<A> a_;
         public:
          B(const Ref<KeyVal> &keyval):
            f1_(keyval->doublevalue("f1")),
            a_(new PrefixKeyVal(keyval,"a"))
          {}
       };

        can be used to read ParsedKeyVal input that looks like

       b<B>: (
         f1 = 1.0
         a<A>: (
           f0 = 2.0
         )
       )

Author

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