Documentation
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Overview ¶
Package calc implements 公式/计算变量 (calc / formula tags): a derived tag whose live value is an expression evaluated over other tags.
A CalcTag names an Output tag, an Expr, and the Input tags the expression reads. Each Input name is used verbatim as an identifier inside Expr, so the Inputs MUST be simple identifiers — no dots, no paths (e.g. "a", "level", not "plant.a") — because a dot inside an expr expression means field access, not a tag name. The expression is compiled once; whenever any Input changes, the Output tag is recomputed.
Example:
e := calc.NewEngine(db)
e.Add(calc.CalcTag{Output: "avg", Expr: "(a + b) / 2", Inputs: []string{"a", "b"}})
db.SetValue("a", 10.0)
db.SetValue("b", 20.0) // -> tag "avg" == 15
Expressions use github.com/expr-lang/expr. Inputs are fed to the expression as float64 (via core.Value.Float); the result is coerced back to float64 for the Output tag.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type CalcTag ¶
type CalcTag struct {
Output string // name of the tag that receives the computed value
Expr string // expression over the Input identifiers
Inputs []string // input tag names, each a simple (dot-free) identifier
}
CalcTag declares one derived tag: Output = Expr evaluated over Inputs.
Inputs are referenced by name as bare identifiers in Expr (e.g. Expr:"(a + b) / 2", Inputs:[]string{"a","b"}) and therefore MUST be simple identifiers without dots.
type Engine ¶
type Engine struct {
// contains filtered or unexported fields
}
Engine wires CalcTags into a core.TagDB: it compiles each expression and keeps the Output tags recomputed as their Inputs change. Add and RemoveAll are safe for concurrent use.
Source Files