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Programming Languages
Janyl Jumadinova September 24, 2020
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Name, Scope, and Binding
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Programming Languages Janyl Jumadinova September 24, 2020 Janyl - - PowerPoint PPT Presentation
Programming Languages Janyl Jumadinova September 24, 2020 Janyl - - PowerPoint PPT Presentation
Programming Languages Janyl Jumadinova September 24, 2020 Janyl Jumadinova Programming Languages September 24, 2020 1 / 17 Name, Scope, and Binding Janyl Jumadinova Programming Languages September 24, 2020 2 / 17 Name, Scope, and Binding
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Name, Scope, and Binding
A name is exactly what you think it is – Most names are identifiers – symbols (like ‘+’) can also be names
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Name, Scope, and Binding
A name is exactly what you think it is – Most names are identifiers – symbols (like ‘+’) can also be names A binding is an association between two things, such as a name and the thing it names.
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Name, Scope, and Binding
A name is exactly what you think it is – Most names are identifiers – symbols (like ‘+’) can also be names A binding is an association between two things, such as a name and the thing it names. The scope of a binding is the part of the program (textually) in which the binding is active.
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Binding
Binding Time: the point at which a binding is created or, more generally, the point at which any implementation decision is made.
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Binding
Binding Time: the point at which a binding is created or, more generally, the point at which any implementation decision is made. language design time program structure, possible type language implementation time
- I/O, arithmetic overflow, type equality (if unspecified in manual)
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Other Implementation Decisions
program writing time – algorithms, names
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Other Implementation Decisions
program writing time – algorithms, names compile time – plan for data layout
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Other Implementation Decisions
program writing time – algorithms, names compile time – plan for data layout link time –layout of whole program in memory
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Other Implementation Decisions
program writing time – algorithms, names compile time – plan for data layout link time –layout of whole program in memory load time
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More Implementation Decisions
run time – value/variable bindings, sizes of strings – NOTE: run time includes
program start-up time module entry time elaboration time (point at which a declaration is first “seen”) procedure entry time
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Binding
The terms STATIC and DYNAMIC are generally used to refer to things bound before run time and at run time, respectively. – “static is a coarse term; so is “dynamic”
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Binding
The terms STATIC and DYNAMIC are generally used to refer to things bound before run time and at run time, respectively. – “static is a coarse term; so is “dynamic” Binding Times are very important in programming languages!
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Binding
In general, early binding times are associated with greater efficiency Later binding times are associated with greater flexibility
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Binding
In general, early binding times are associated with greater efficiency Later binding times are associated with greater flexibility Compiled languages tend to have early binding times Interpreted languages tend to have later binding times
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Scope Rules - Control Bindings
Fundamental to all programming languages is the ability to name data
- i.e., to refer to data using symbolic identifiers rather than addresses
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Scope Rules - Control Bindings
Fundamental to all programming languages is the ability to name data
- i.e., to refer to data using symbolic identifiers rather than addresses
Not all data is named! For example, dynamic storage in C or Pascal is referenced by pointers, not names
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Scope Rules - Control Bindings
Fundamental to all programming languages is the ability to name data
- i.e., to refer to data using symbolic identifiers rather than addresses
Not all data is named! For example, dynamic storage in C or Pascal is referenced by pointers, not names double *d = (double *)malloc(8); *d = 3.14; /* No name is bound to the value 3.14 */ /* The name ‘‘d’’ is bound to the ADDRESS containing 3.14 */
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Lifetime and Storage Management
The period of time from creation to destruction is called the LIFETIME of a binding.
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Lifetime and Storage Management
The period of time from creation to destruction is called the LIFETIME of a binding. If object outlives binding it’s garbage. If binding outlives object it’s a dangling reference.
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Lifetime and Storage Management
The period of time from creation to destruction is called the LIFETIME of a binding. If object outlives binding it’s garbage. If binding outlives object it’s a dangling reference. The textual region of the program in which the binding is active is its scope.
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Lifetime and Storage Management
Storage Allocation mechanisms Static Stack Heap
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Lifetime and Storage Management
Storage Allocation mechanisms Static Stack Heap Static allocation for code globals static or own variables
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Static Example
In C, variables can be global (visible to any function)
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Static Example
When we compile this, i is stored in a fixed location, while j is allocated
- n the stack
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Two Types of Scoping
Static scoping (also called “lexical scoping”) most familiar (Java, C) scope of variables known at compile time
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Two Types of Scoping
Static scoping (also called “lexical scoping”) most familiar (Java, C) scope of variables known at compile time Dynamic scoping scope depends on order of function calls at execution time pretty rare nowadays
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Static Scope Example (Java)
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What Happens Here? (Java)
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What Happens in Dynamic Scoping?
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In-Class Exercise
JavaScript Case Study
– Pull activity4 in your class activities repository
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