Expression kinds #5628
Expression kinds #5628
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| type ConstantExpression = { | ||
| kind: 'constant', | ||
| evaluate: (globals: GlobalProperties, feature?: Feature) => any |
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It's not feasible yet, but I hope to be able to specialize the evaluate method appropriately for the various kinds in a later commit. For example, constant expression evaluation should require no arguments, and the Feature argument should not be optional for source and composite expression evaluation.
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Once this happens, we'll need a way to heatmap-color.
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| type ConstantExpression = { | ||
| kind: 'constant', | ||
| evaluate: (globals: GlobalProperties, feature?: Feature) => any |
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Once this happens, we'll need a way to heatmap-color.
src/style-spec/expression/index.js
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| type SourceExpression = { | ||
| result: 'source', | ||
| evaluate: (globals: GlobalProperties, feature?: Feature) => any, | ||
| }; |
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What do you think about FeatureExpression? Seems more direct to me, but maybe there was a reason we opted for SourceFunction over FeatureFunction before...
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#5531 suggests DataExpression -- let's hash out terminology there. For now, I'm happy just getting JS consistent with current native terms. 😄
| return isFeatureConstant ? { | ||
| functionType: 'constant', | ||
| layoutSize: layer.getLayoutValue(sizeProperty, {zoom: tileZoom + 1}) | ||
| } : { functionType: 'source' }; | ||
| } | ||
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| // calculate covering zoom stops for zoom-dependent values | ||
| const levels = declaration.expression.zoomStops; | ||
| const levels = (declaration.expression: any).zoomStops; |
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This any cast is justified by the !declaration || declaration.isZoomConstant() check above, right? Let's include a line comment indicating that.
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Yeah. For #2739 this code is going to get rewritten in cases over expression.kind, without any casts required, so I'm just going to leave it for now.
jfirebaugh
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Introduce the same sort of discriminated union as is used in native: an expression (or function, or generally, any property value) has one of the following kinds:
constant,camera,source,composite.This is a prerequisite for #2739 / #3044.