Rust Expressions and Declarations in System Software Development
E81 CSE 542S:
Concurrency and Memory Safe
System Software Development
Department of Computer Science & Engineering
1
Chris Gill
cdgill@wustl.edu
Expressions
Expressions in Rust
•
Rust is an
expression language
–
So, most things in Rust have values
–
E.g., ending a function with
Ok(())
(and no
semicolon) generates its return value
•
Expressions have execution semantics
–
E.g., operator precedence as well as
associativity, implicitly as well as explicitly
2
CSE 542S – Concurrency and Memory Safe System Software Development
Blocks and Semicolons
•
A block encapsulates a sequence of
expressions and produces a value
–
E.g.,
None => {println!(“all good”); Ok(())}•
A semicolon drops an expression’s value
–
Useful if default expression type isn’t what
you want (e.g.,
if
without
else
returns
()
)
3
CSE 542S – Concurrency and Memory Safe System Software Development
Declarations
•
Some declarations introduce functions,
structs, and other
items
•
Variable declarations give a name and
optionally a type and initializer
–
The compiler often can figure out the type
and default initialization if they’re omitted
–
The initialization value may come from a
function result, block, or other expression
4
CSE 542S – Concurrency and Memory Safe System Software Development
Conditional Expressions
•
Blocks can be nested using
if
and
else
–
All branches must return the same type
–
E.g.,
if i > j {i} else {j}•
The
if let
form captures the result of a
function call, expression, etc. as well
–
E.g.,
if let Err(err) = myfunc()
{log(err);} else {process_result();}5
CSE 542S – Concurrency and Memory Safe System Software Development
Multi-case Expressions
•
A
match
expression is similar to a switch
or case statement in other languages
•
You must cover all cases either explicitly
or via the default match pattern
_
•
The patterns are evaluated in the order
they are given (earlier has precedence)
•
Also can destructure tuples using match
–
E.g.,
match t {(x, y) => do_func(x,y);}6
CSE 542S – Concurrency and Memory Safe System Software Development
Iteration Expressions
•
The
while
and
for
expressions don’t,
but
loop
lets you specify/return a value
–
E.g.,
loop {if done() break val;}•
Like an
if let
expression, a
while let
expression also captures a value
•
A
for
expression uses closed/open
ranges, consumes non-copy types values
–
This suggests using references to iterate
over collections of variables (e.g., in vector)
7
CSE 542S – Concurrency and Memory Safe System Software Development
Studio 5
•
Revisit operator precedence and associativity
•
Explore how to capture/use expression values
•
Examine how reference vs. move semantics
play into iteration over collections
•
Studios 1 through 11 are due by 11:59pm on
the night before Exam 1
–
Submit as soon as each is done so you get feedback
–
… and can resubmit any that may be marked
incomplete
8
CSE 542S – Concurrency and Memory Safe System Software Development
Rust is an expression language where most things have values. Learn about Rust expressions, blocks, declarations, conditional expressions, multi-case expressions, and iteration expressions in system software development. Explore the execution semantics, syntax, and best practices for writing safe and efficient code in Rust.
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Presentation Transcript
E81 CSE 542S: Concurrency and Memory Safe System Software Development Expressions Department of Computer Science & Engineering Chris Gill cdgill@wustl.edu 1
Expressions in Rust Rust is an expression language So, most things in Rust have values E.g., ending a function with Ok(()) (and no semicolon) generates its return value Expressions have execution semantics E.g., operator precedence as well as associativity, implicitly as well as explicitly 2 CSE 542S Concurrency and Memory Safe System Software Development
Blocks and Semicolons A block encapsulates a sequence of expressions and produces a value E.g., None => {println!( all good ); Ok(())} A semicolon drops an expression s value Useful if default expression type isn t what you want (e.g., if without else returns ()) 3 CSE 542S Concurrency and Memory Safe System Software Development
Declarations Some declarations introduce functions, structs, and other items Variable declarations give a name and optionally a type and initializer The compiler often can figure out the type and default initialization if they re omitted The initialization value may come from a function result, block, or other expression 4 CSE 542S Concurrency and Memory Safe System Software Development
Conditional Expressions Blocks can be nested using if and else All branches must return the same type E.g., if i > j {i} else {j} The if let form captures the result of a function call, expression, etc. as well E.g., if let Err(err) = myfunc() {log(err);} else {process_result();} 5 CSE 542S Concurrency and Memory Safe System Software Development
Multi-case Expressions A match expression is similar to a switch or case statement in other languages You must cover all cases either explicitly or via the default match pattern _ The patterns are evaluated in the order they are given (earlier has precedence) Also can destructure tuples using match E.g., match t {(x, y) => do_func(x,y);} 6 CSE 542S Concurrency and Memory Safe System Software Development
Iteration Expressions The while and forexpressions don t, but loop lets you specify/return a value E.g., loop {if done() break val;} Like an if let expression, a while let expression also captures a value A for expression uses closed/open ranges, consumes non-copy types values This suggests using references to iterate over collections of variables (e.g., in vector) 7 CSE 542S Concurrency and Memory Safe System Software Development
Studio 5 Revisit operator precedence and associativity Explore how to capture/use expression values Examine how reference vs. move semantics play into iteration over collections Studios 1 through 11 are due by 11:59pm on the night before Exam 1 Submit as soon as each is done so you get feedback and can resubmit any that may be marked incomplete 8 CSE 542S Concurrency and Memory Safe System Software Development
