stats manual in README

Pointer vs. value receivers are... interesting.

README.md

@@ -42,7 +42,7 @@ A bucket of game state.
 
 ### Stat
 
-An arbitrary variable (or function, if it's calculated) tagged with some stuff to make it easier to display to the player.
+An arbitrary variable (or function, if it's calculated) tagged with some stuff to make it easier to display to the player. Stats can be extracted automatically (see "Stat Extraction" below).
 
 ### StatsCollection
 
@@ -57,3 +57,26 @@ There are some special errors that Rules can use to "communicate with" the rule
 ### Messages
 
 For now, strings but inconvenient. Intended to provide forwards compatibility when we eventually include some way to format text, where all the stuff written for "it's just a string" would break if not for having this extra type in the way to wrap it where we can stay compatible with "it's just a string" mode.
+
+## Stat Extraction
+The function `ExtractStats` creates a stats list automatically by searching through a struct's fields and methods. The following things are recognized as stats:
+
+* any method with a name like `StatFoo` or `HiddenStatFoo` (the latter are marked as invisible stats, which show up only in debug mode with the implementation in BasicStatsPane)
+* any exported field with a type that is already a `Stat`; the `Stored[T]` and `Hidden[T]` generic types are containers for this
+* any exported field tagged with `cardsim:"stat"`
+    * or `cardsim:"hidden"` for hidden stats. `"hiddenstat"` also works.
+    * you can use `"round2"` to round to two decimal places -- you can use any integer here, not just 2. works with both `float` types.
+    * `"hiddenround3"` (or any other number) creates a hidden rounded stat.
+    * To change the display name of a stat, use a separate tag phrase in addition to the stat tag, `cardsim_name:"name"`.
+        * For example: `cardsim:"stat" cardsim_name:"Stat Display Name"` creates a visible stat that shows up as "Stat Display Name".
+        * `cardsim:"hiddenround1" cardsim_name:"Hidden Rounded Stat"` creates an invisible stat that shows up, rounded to one decimal place, as "Hidden Rounded Stat".
+
+Stat extraction can implement most or all of your type's `Stats` method for you:
+
+```
+func (e *ExampleType) Stats() []cardsim.Stat {
+    return cardsim.ExtractStats(e)
+}
+```
+
+ExtractStats puts methods first (lexicographically), then fields (in the order they appear). You can use `cardsim.SortStats` to instead put visible stats before hidden stats, alphabetized (case-insensitive).

cardsim/stats.go

@@ -4,7 +4,11 @@ import (
 	"fmt"
 	"reflect"
 	"sort"
+	"strconv"
 	"strings"
+	"unicode"
+
+	"golang.org/x/exp/constraints"
 )
 
 // A StatsCollection contains stats.
@@ -114,9 +118,30 @@ func (s statFunc[T]) Visible() bool {
 	return s.visible
 }
 
-// ExtractStats pulls all exported Stat fields (not functions) out of a struct.
-// If x cannot be resolved to a struct, it panics. It unwraps interfaces and
-// follows pointers to try to find a struct.
+// ExtractStats pulls all exported stats out of a struct. It puts methods before
+// fields. If the calculated name of a method conflicts with the calculated
+// name of a stat from a field, the method wins.
+//
+// A field is a stat if it is of some Stat type or is tagged with `cardsim:"stat"`,
+// `cardsim:"hidden"` (invisible stat), `cardsim:"round2"` (or any integer, 2 is
+// just an example), or `cardsim:"hiddenround3"`. `hiddenstat`, `statround`, and
+// `hiddenstatround` are also accepted, but other orders of these directives
+// are not. A "round" stat must be a float type and it will be rounded to
+// this number of decimal places.
+//
+// A method is a Stat if it takes 0 arguments, returns exactly 1 value, and
+// starts with Stat or HiddenStat.
+//
+// The name of these inferred stats is calculated by breaking the name into
+// separate words before each capital letter, unless there are consecutive
+// capital letters, which it interprets as an initialism (followed by the
+// start of another word, if it's not at the end). To insert a space between
+// consecutive capital letters, insert an underscore (`_`). This name inference
+// trims "Stat" and "HiddenStat" off the front of method names.
+//
+// To override the name extracted from a field name, add `cardsim_name:"name"`
+// to the tag, where the name part is the name you want to use. It will not be
+// formatted further - use normal spaces, capitalization, etc.
 func ExtractStats(x any) []Stat {
 	v := reflect.ValueOf(x)
 	for k := v.Kind(); k == reflect.Pointer || k == reflect.Interface; k = v.Kind() {
@@ -125,19 +150,125 @@ func ExtractStats(x any) []Stat {
 	if v.Kind() != reflect.Struct {
 		panic(fmt.Errorf("%T is not a struct", x))
 	}
+	typ := v.Type()
 
 	var ret []Stat
-	lim := v.NumField()
+
+	known := make(map[string]bool)
+	for _, vv := range []reflect.Value{v, v.Addr()} {
+		xt := vv.Type()
+		lim := xt.NumMethod()
 		for i := 0; i < lim; i++ {
-		f := v.Field(i)
+			m := xt.Method(i)
+			if !m.IsExported() {
+				continue
+			}
+			tm := m.Type
+			if tm.NumIn() != 1 {
+				// 1 arg -- receiver
+				continue
+			}
+			if tm.NumOut() != 1 {
+				continue
+			}
+			nameParts := explode(m.Name)
+			if len(nameParts) < 2 {
+				continue
+			}
+			isHidden := false
+			if nameParts[0] == "Hidden" {
+				isHidden = true
+				nameParts = nameParts[1:]
+			}
+			if nameParts[0] != "Stat" {
+				continue
+			}
+			n := strings.Join(nameParts[1:], " ")
+			if n == "" {
+				continue
+			}
+			if known[n] {
+				continue
+			}
+			known[n] = true
+			val := vv.Method(i).Call([]reflect.Value{})
+			if len(val) != 1 {
+				// This shouldn't happen - we already checked Out. Weird.
+				continue
+			}
+			if !val[0].CanInterface() {
+				continue
+			}
+			ret = append(ret, &StatLiteral{
+				Name:      n,
+				Value:     fmt.Sprint(val[0].Interface()),
+				IsVisible: !isHidden,
+			})
+		}
+	}
+
+	fields := reflect.VisibleFields(typ)
+	for _, sf := range fields {
+		if !sf.IsExported() {
+			continue
+		}
+		f := v.FieldByIndex(sf.Index)
 		if !f.CanInterface() {
 			continue
 		}
-		x := f.Interface()
-		if s, ok := x.(Stat); ok {
+		iface := f.Interface()
+		if s, ok := iface.(Stat); ok {
+			if known[s.StatName()] {
+				continue
+			}
+			known[s.StatName()] = true
 			ret = append(ret, s)
+			continue
 		}
+		if t := sf.Tag.Get("cardsim"); t != "" {
+			isStat := false
+			isHidden := false
+			t = strings.ToLower(t)
+			t = strings.TrimSpace(t)
+			if strings.HasPrefix(t, "hidden") {
+				isStat = true
+				isHidden = true
+				t = t[6:]
 			}
+			if strings.HasPrefix(t, "stat") {
+				isStat = true
+				t = t[4:]
+			}
+			var val string
+			if strings.HasPrefix(t, "round") {
+				isStat = true
+				t = t[5:]
+				n, _ := strconv.Atoi(t)
+				fs := fmt.Sprintf("%%.%df", n)
+				val = fmt.Sprintf(fs, iface)
+			} else if isStat {
+				val = fmt.Sprint(iface)
+			} else {
+				continue // not identifiably a stat
+			}
+			nm := strings.Join(explode(sf.Name), " ")
+			if t := sf.Tag.Get("cardsim_name"); t != "" {
+				nm = t
+			}
+			if known[nm] {
+				continue
+			}
+			known[nm] = true
+			ret = append(ret, &StatLiteral{
+				Name:      nm,
+				Value:     val,
+				IsVisible: !isHidden,
+			})
+			continue
+		}
+		// Else, not a stat.
+	}
+
 	return ret
 }
 
@@ -173,3 +304,105 @@ func (s statSorter) Less(i, j int) bool {
 	// Names differ only by capitalization, if that.
 	return lhs.StatName() < rhs.StatName()
 }
+
+// StatLiteral stores a ready-to-emit stat value.
+type StatLiteral struct {
+	Name      string
+	Value     string
+	IsVisible bool
+}
+
+func (s *StatLiteral) StatName() string {
+	return s.Name
+}
+
+func (s *StatLiteral) String() string {
+	return s.Value
+}
+
+func (s *StatLiteral) Visible() bool {
+	return s.IsVisible
+}
+
+func EmitStat(name string, v any) *StatLiteral {
+	return &StatLiteral{
+		Name:      name,
+		Value:     fmt.Sprint(v),
+		IsVisible: true,
+	}
+}
+
+func EmitHiddenStat(name string, v any) *StatLiteral {
+	return &StatLiteral{
+		Name:      name,
+		Value:     fmt.Sprint(v),
+		IsVisible: false,
+	}
+}
+
+func Statf(name string, f string, args ...any) *StatLiteral {
+	return &StatLiteral{
+		Name:      name,
+		Value:     fmt.Sprintf(f, args...),
+		IsVisible: true,
+	}
+}
+
+func HiddentStatf(name string, f string, args ...any) *StatLiteral {
+	return &StatLiteral{
+		Name:      name,
+		Value:     fmt.Sprintf(f, args...),
+		IsVisible: false,
+	}
+}
+
+func RoundStat[N constraints.Float](name string, val N, decimals int) *StatLiteral {
+	f := fmt.Sprintf("%%.%df", decimals)
+	return &StatLiteral{
+		Name:      name,
+		Value:     fmt.Sprintf(f, val),
+		IsVisible: true,
+	}
+}
+
+func RoundHiddenStat[N constraints.Float](name string, val N, decimals int) *StatLiteral {
+	r := RoundStat(name, val, decimals)
+	r.IsVisible = false
+	return r
+}
+
+// explode turns CamelCase into multiple strings. It recognizes initialisms. To
+// split consecutive capital letters into separate words instead of recognizing
+// them as an initialism, insert underscores.
+func explode(s string) []string {
+	var parts []string
+	started := 0
+	initialism := false
+	for i, r := range s {
+		if unicode.IsUpper(r) {
+			if initialism || (started == i) {
+				continue
+			}
+			if started == i-1 {
+				initialism = true
+				continue
+			}
+			parts = append(parts, s[started:i])
+			started = i
+			continue
+		}
+		if r == '_' {
+			parts = append(parts, s[started:i])
+			initialism = false
+			started = i + 1
+			continue
+		}
+		if initialism {
+			parts = append(parts, s[started:i-1])
+			initialism = false
+			started = i - 1
+		}
+	}
+	parts = append(parts, s[started:])
+	return parts
+}

go.mod

@@ -7,4 +7,5 @@ require github.com/kr/pretty v0.3.1
 require (
 	github.com/kr/text v0.2.0 // indirect
 	github.com/rogpeppe/go-internal v1.9.0 // indirect
+	golang.org/x/exp v0.0.0-20230321023759-10a507213a29
 )

go.sum

@@ -6,3 +6,5 @@ github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
 github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e/go.mod h1:pJLUxLENpZxwdsKMEsNbx1VGcRFpLqf3715MtcvvzbA=
 github.com/rogpeppe/go-internal v1.9.0 h1:73kH8U+JUqXU8lRuOHeVHaa/SZPifC7BkcraZVejAe8=
 github.com/rogpeppe/go-internal v1.9.0/go.mod h1:WtVeX8xhTBvf0smdhujwtBcq4Qrzq/fJaraNFVN+nFs=
+golang.org/x/exp v0.0.0-20230321023759-10a507213a29 h1:ooxPy7fPvB4kwsA2h+iBNHkAbp/4JxTSwCmvdjEYmug=
+golang.org/x/exp v0.0.0-20230321023759-10a507213a29/go.mod h1:CxIveKay+FTh1D0yPZemJVgC/95VzuuOLq5Qi4xnoYc=

smoketest/cards.go

@@ -85,7 +85,7 @@ func (i inverseDivision) OptionText(p *player) (cardsim.Message, error) {
 
 func (i inverseDivision) Enact(p *player) (cardsim.Message, error) {
 	if p.Stats.Number.Value == 0 {
-		return nil, errors.New("you can't divide by zero!")
+		return nil, errors.New("you can't divide by zero")
 	}
 	p.Stats.Number.Value = int(i) / p.Stats.Number.Value
 	return cardsim.MsgStr("Inverse divided."), nil

smoketest/collection.go

@@ -11,6 +11,11 @@ type SmokeTestCollection struct {
 	Turns  cardsim.Invisible[int]
 
 	Flavor cardsim.Stored[string]
+
+	Things       int     `cardsim:"stat" cardsim_name:"A Renamed Thing"`
+	MoreThings   int     `cardsim:"hidden"`
+	FloatyThings float64 `cardsim:"round1"`
+	Label        string  `cardsim:"stat"`
 }
 
 func (c *SmokeTestCollection) Average() float64 {
@@ -23,3 +28,7 @@ func (c *SmokeTestCollection) Stats() []cardsim.Stat {
 	cardsim.SortStats(stats)
 	return stats
 }
+
+func (c *SmokeTestCollection) StatTotalThings() float64 {
+	return float64(c.Things+c.MoreThings) + c.FloatyThings
+}

smoketest/main.go

@@ -28,6 +28,10 @@ func main() {
 				Name:  "Flavor",
 				Value: "Lemon",
 			},
+			Things:       5,
+			MoreThings:   9,
+			FloatyThings: 123.456,
+			Label:        "whee",
 		},
 	)
 	p.Name = "Dave"