feat(examples): add p/demo/squid

examples/gno.land/p/demo/squid/README.md

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+# squid
+
+```
+package squid // import "gno.land/p/demo/squid"
+
+Package squid provides a simple way to have sequential IDs which will be ordered
+correctly when inserted in an AVL tree.
+
+Sample usage:
+
+    var id squid.ID
+    var users avl.Tree
+
+    func NewUser() {
+    	users.Set(id.Next().Binary(), &User{ ... })
+    }
+
+TYPES
+
+type ID uint64
+    An ID is a simple sequential ID generator.
+
+func FromBinary(b string) (ID, bool)
+    FromBinary creates a new ID from the given string.
+
+func (i ID) Binary() string
+    Binary returns a big-endian binary representation of the ID, suitable to be
+    used as an AVL key.
+
+func (i *ID) Next() ID
+    Next advances the ID i. It will panic if increasing ID would overflow.
+
+func (i *ID) TryNext() (ID, bool)
+    TryNext increases i by 1 and returns its value. It returns true if
+    successful, or false if the increment would result in an overflow.
+```

examples/gno.land/p/demo/squid/gno.mod

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+module gno.land/p/demo/squid

examples/gno.land/p/demo/squid/squid.gno

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+// Package squid provides a simple way to have sequential IDs which will be
+// ordered correctly when inserted in an AVL tree.
+//
+// Sample usage:
+//
+//	var id squid.ID
+//	var users avl.Tree
+//
+//	func NewUser() {
+//		users.Set(id.Next().Binary(), &User{ ... })
+//	}
+package squid
+
+import "encoding/binary"
+
+// An ID is a simple sequential ID generator.
+type ID uint64
+
+// Next advances the ID i.
+// It will panic if increasing ID would overflow.
+func (i *ID) Next() ID {
+	next, ok := i.TryNext()
+	if !ok {
+		panic("squid: next ID overflows uint64")
+	}
+	return next
+}
+
+const maxUint64 uint64 = 1<<64 - 1
+
+// TryNext increases i by 1 and returns its value.
+// It returns true if successful, or false if the increment would result in
+// an overflow.
+func (i *ID) TryNext() (ID, bool) {
+	if *i == maxUint64 {
+		// Addition will overflow.
+		return 0, false
+	}
+	*i++
+	return *i, true
+}
+
+// Binary returns a big-endian binary representation of the ID,
+// suitable to be used as an AVL key.
+func (i ID) Binary() string {
+	buf := make([]byte, 8)
+	binary.BigEndian.PutUint64(buf, uint64(i))
+	return string(buf)
+}
+
+// FromBinary creates a new ID from the given string.
+func FromBinary(b string) (ID, bool) {
+	if len(b) != 8 {
+		return 0, false
+	}
+	return ID(binary.BigEndian.Uint64([]byte(b))), true
+}

examples/gno.land/p/demo/squid/squid_test.gno

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+package squid
+
+import (
+	"strings"
+	"testing"
+	"fmt"
+)
+
+func TestID(t *testing.T) {
+	var i ID
+
+	for j := 0; j < 100; j++ {
+		i.Next()
+	}
+	if i != 100 {
+		t.Fatalf("invalid: wanted %d got %d", 100, i)
+	}
+}
+
+func TestID_Overflow(t *testing.T) {
+	i := ID(maxUint64)
+
+	defer func() {
+		err := recover()
+		if !strings.Contains(fmt.Sprint(err), "next ID overflows") {
+			t.Errorf("did not overflow")
+		}
+	}()
+
+	i.Next()
+}
+
+func TestID_Binary(t *testing.T) {
+	var i ID
+	prev := i.Binary()
+
+	for j := 0; j < 1000; j++ {
+		cur := i.Next().Binary()
+		if cur <= prev {
+			t.Fatalf("cur %x <= prev %x", cur, prev)
+		}
+	}
+}