3.7: Primitives and Pragmas

Last updated
Save as PDF

Page ID: 37618

Andrew P. Black, Stéphane Ducasse, Oscar Nierstrasz, Damien Pollet

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

In Smalltalk everything is an object, and everything happens by sending messages. Nevertheless, at certain points we hit rock bottom. Certain objects can only get work done by invoking virtual machine primitives.

For example, the following are all implemented as primitives: memory allocation (new, new:), bit manipulation (bitAnd:, bitOr:, bitShift:), pointer and integer arithmetic (+, --, <, >, *, / , =, ==...), and array access (at:, at:put:).

Primitives are invoked with the syntax <primitive: aNumber>. A method that invokes such a primitive may also include Smalltalk code, which will be evaluated only if the primitive fails.

Here we see the code for SmallInteger\(\gg\)+. If the primitive fails, the expression super + aNumber will be evaluated and returned.

+ aNumber
    "Primitive. Add the receiver to the argument and answer with the result
    if it is a SmallInteger. Fail if the argument or the result is not a
    SmallInteger Essential No Lookup. See Object documentation whatIsAPrimitive."

    <primitive: 1>
    ↑ super + aNumber

Since Squeak 3.9, the angle bracket syntax is also used for method annotations called pragmas.