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One of the proposals in #23328 This PR introduces a simple expression calculator (templates/eval/eval.go), it can do basic expression calculations. Many untested template helper functions like `Mul` `Add` can be replaced by this new approach. Then these `Add` / `Mul` / `percentage` / `Subtract` / `DiffStatsWidth` could all use this `Eval`. And it provides enhancements for Golang templates, and improves readability. Some examples: ---- * Before: `{{Add (Mul $glyph.Row 12) 12}}` * After: `{{Eval $glyph.Row "*" 12 "+" 12}}` ---- * Before: `{{if lt (Add $i 1) (len $.Topics)}}` * After: `{{if Eval $i "+" 1 "<" (len $.Topics)}}` ## FAQ ### Why not use an existing expression package? We need a highly customized expression engine: * do the calculation on the fly, without pre-compiling * deal with int/int64/float64 types, to make the result could be used in Golang template. * make the syntax could be used in the Golang template directly * do not introduce too much complex or strange syntax, we just need a simple calculator. * it needs to strictly follow Golang template's behavior, for example, Golang template treats all non-zero values as truth, but many 3rd packages don't do so. ### What's the benefit? * Developers don't need to add more `Add`/`Mul`/`Sub`-like functions, they were getting more and more. Now, only one `Eval` is enough for all cases. * The new code reads better than old `{{Add (Mul $glyph.Row 12) 12}}`, the old one isn't familiar to most procedural programming developers (eg, the Golang expression syntax). * The `Eval` is fully covered by tests, many old `Add`/`Mul`-like functions were never tested. ### The performance? It doesn't use `reflect`, it doesn't need to parse or compile when used in Golang template, the performance is as fast as native Go template. ### Is it too complex? Could it be unstable? The expression calculator program is a common homework for computer science students, and it's widely used as a teaching and practicing purpose for developers. The algorithm is pretty well-known. The behavior can be clearly defined, it is stable.
24 lines
1.5 KiB
Handlebars
24 lines
1.5 KiB
Handlebars
<div id="rel-container">
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<svg viewbox="{{Eval .Graph.MinColumn "*" 5}} {{Eval .Graph.MinRow "*" 12}} {{Eval .Graph.Width "*" 5 "+" 5}} {{Eval .Graph.Height "*" 12}}" width="{{Eval .Graph.Width "*" 10 "+" 10}}px">
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{{range $flowid, $flow := .Graph.Flows}}
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<g id="flow-{{$flow.ID}}" class="flow-group flow-color-{{$flow.ColorNumber}} flow-color-16-{{$flow.Color16}}" data-flow="{{$flow.ID}}" data-color="{{$flow.ColorNumber}}">
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<path d="{{range $i, $glyph := $flow.Glyphs -}}
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{{- if or (eq $glyph.Glyph '*') (eq $glyph.Glyph '|') -}}
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M {{Eval $glyph.Column "*" 5 "+" 5}} {{Eval $glyph.Row "*" 12 "+" 0}} v 12 {{/* */ -}}
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{{- else if eq $glyph.Glyph '/' -}}
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M {{Eval $glyph.Column "*" 5 "+" 10}} {{Eval $glyph.Row "*" 12 "+" 0}} l -10 12 {{/* */ -}}
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{{- else if eq $glyph.Glyph '\\' -}}
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M {{Eval $glyph.Column "*" 5 "+" 0}} {{Eval $glyph.Row "*" 12 "+" 0}} l 10 12 {{/* */ -}}
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{{- else if or (eq $glyph.Glyph '-') (eq $glyph.Glyph '.') -}}
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M {{Eval $glyph.Column "*" 5 "+" 0}} {{Eval $glyph.Row "*" 12 "+" 12}} h 5 {{/* */ -}}
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{{- else if eq $glyph.Glyph '_' -}}
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M {{Eval $glyph.Column "*" 5 "+" 0}} {{Eval $glyph.Row "*" 12 "+" 12}} h 10 {{/* */ -}}
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{{- end -}}
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{{- end}}" stroke-width="1" fill="none" id="flow-{{$flow.ID}}-path" stroke-linecap="round"></path>
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{{range $flow.Commits}}
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<circle class="flow-commit" cx="{{Eval .Column "*" 5 "+" 5}}" cy="{{Eval .Row "*" 12 "+" 6}}" r="2.5" stroke="none" id="flow-commit-{{.Rev}}" data-rev="{{.Rev}}"></circle>
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{{end}}
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</g>
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{{end}}
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</svg>
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</div>
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