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3.7: Primitives and Pragmas

  • Page ID
    37618
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    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.


    This page titled 3.7: Primitives and Pragmas is shared under a CC BY-SA 3.0 license and was authored, remixed, and/or curated by Andrew P. Black, Stéphane Ducasse, Oscar Nierstrasz, Damien Pollet via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.