1. CSE 425: Semantics II Implementing Scopes A symbol table is in essence a dictionary –I.e., every name appears in it, with the info known about it –Usually expressed as a name and an attribute list/map/etc. Symbol table entries are added, modified, looked up –I.e., as a name is declared, then defined, then used, etc. A symbol table can have other operations as well –Scope entry and exit operations (may navigate within it) Symbol tables often implemented in 1 of 2 main ways –An association list (of name/value pairs) is often simplest –A central reference table maintains an explicit mapping

2. CSE 425: Semantics II Symbol Tables for Nested Scopes Scope analysis allows declarations and bindings to be processed in a stack-like manner at run-time –A symbol table is used to keep track of that information –E.g., each identifier in a scope has a set of bindings –Structure/management may range from a single static symbol table to a dynamic hierarchy of per-scope tables pi double3.141 argc int2 argv char ** function scope main (int, char**) global scope

3. CSE 425: Semantics II Names, Aliases, and Overloading Multiple names may refer to same object or variable –E.g., pointers or references (and pass-by-reference) in C++ The ability to re-use a name is also commonplace –E.g., using the + operator for addition or string concatenation –Since a symbol table usually stores parameter type attributes for a function identifier, can use to resolve –I.e., look up the declaration/definition of a function or operator based on its parameter types as well as its name Many languages allow function name overloading and a smaller number of them allow operator overloading –Syntactically introduced constraints such as precedence and associativity of operators must be respected (unless waived) –Though with tweaks like C++ prefix operator+ call syntax

4. CSE 425: Semantics II Coercion and Polymorphism Types often are allowed to be converted to other types –E.g., while (ifs >> token) // ifstream& to bool When the complier forces this to happen its coercion –I.e., the type conversion happens implicitly Polymorphism lets multiple unconverted types be used –Inheritance polymorphism (E.g., C++ classes) –Interface polymorphism (E.g., C++ templates) –Both support subtype polymorphism (Liskov substitution) Explicit parametric polymorphism is called “generic” –E.g., C++ templates with specialization

5. CSE 425: Semantics II Binding of Reference Environments Referencing environment depends on the order in which declarations are encountered –When is the context in which a function is executed fixed? –This matters because of nesting of scopes, hiding of names, and the ability to pass a function (pointer) as a parameter –Shallow binding is done just before function is called –Deep binding is done when the parameter is first passed Function/subroutine closures –Bundle referencing environment with reference to subroutine –E.g., local variable capture list in C++11 lambda expression Object closures –Similar idea, bundle member variables and operator()

6. CSE 425: Semantics II Today’s Studio Exercises We’ll code up ideas from Scott Chapter 3.4-3.8 –Again looking at the semantics of different C++ constructs –Extending the symbol table from the last studio Today’s exercises are again in C++ –Please take advantage of the on-line reference manual pages that are linked on the course web site –As always, please ask us for help as needed When done, email your answers to the course e-mail account with “Semantics Studio II” in the subject