add skills and CLAUDE.md to enable better llm context management

.claude/skills/golang/references/effective-go-summary.md

@@ -0,0 +1,423 @@
+# Effective Go - Key Points Summary
+
+Source: https://go.dev/doc/effective_go
+
+## Formatting
+
+- Use `gofmt` to automatically format your code
+- Indentation: use tabs
+- Line length: no strict limit, but keep reasonable
+- Parentheses: Go uses fewer parentheses than C/Java
+
+## Commentary
+
+- Every package should have a package comment
+- Every exported name should have a doc comment
+- Comments should be complete sentences
+- Start comments with the name of the element being described
+
+Example:
+```go
+// Package regexp implements regular expression search.
+package regexp
+
+// Compile parses a regular expression and returns, if successful,
+// a Regexp object that can be used to match against text.
+func Compile(str string) (*Regexp, error) {
+```
+
+## Names
+
+### Package Names
+- Short, concise, evocative
+- Lowercase, single-word
+- No underscores or mixedCaps
+- Avoid stuttering (e.g., `bytes.Buffer` not `bytes.ByteBuffer`)
+
+### Getters/Setters
+- Getter: `Owner()` not `GetOwner()`
+- Setter: `SetOwner()`
+
+### Interface Names
+- One-method interfaces use method name + -er suffix
+- Examples: `Reader`, `Writer`, `Formatter`, `CloseNotifier`
+
+### MixedCaps
+- Use `MixedCaps` or `mixedCaps` rather than underscores
+
+## Semicolons
+
+- Lexer automatically inserts semicolons
+- Never put opening brace on its own line
+
+## Control Structures
+
+### If
+```go
+if err := file.Chmod(0664); err != nil {
+    log.Print(err)
+    return err
+}
+```
+
+### Redeclaration
+```go
+f, err := os.Open(name)
+// err is declared here
+
+d, err := f.Stat()
+// err is redeclared here (same scope)
+```
+
+### For
+```go
+// Like a C for
+for init; condition; post { }
+
+// Like a C while
+for condition { }
+
+// Like a C for(;;)
+for { }
+
+// Range over array/slice/map/channel
+for key, value := range oldMap {
+    newMap[key] = value
+}
+
+// If you only need the key
+for key := range m {
+    // ...
+}
+
+// If you only need the value
+for _, value := range array {
+    // ...
+}
+```
+
+### Switch
+- No automatic fall through
+- Cases can be expressions
+- Can switch on no value (acts like if-else chain)
+
+```go
+switch {
+case '0' <= c && c <= '9':
+    return c - '0'
+case 'a' <= c && c <= 'f':
+    return c - 'a' + 10
+case 'A' <= c && c <= 'F':
+    return c - 'A' + 10
+}
+```
+
+### Type Switch
+```go
+switch t := value.(type) {
+case int:
+    fmt.Printf("int: %d\n", t)
+case string:
+    fmt.Printf("string: %s\n", t)
+default:
+    fmt.Printf("unexpected type %T\n", t)
+}
+```
+
+## Functions
+
+### Multiple Return Values
+```go
+func (file *File) Write(b []byte) (n int, err error) {
+    // ...
+}
+```
+
+### Named Result Parameters
+- Named results are initialized to zero values
+- Can be used for documentation
+- Enable naked returns
+
+```go
+func ReadFull(r Reader, buf []byte) (n int, err error) {
+    for len(buf) > 0 && err == nil {
+        var nr int
+        nr, err = r.Read(buf)
+        n += nr
+        buf = buf[nr:]
+    }
+    return
+}
+```
+
+### Defer
+- Schedules function call to run after surrounding function returns
+- LIFO order
+- Arguments evaluated when defer executes
+
+```go
+func trace(s string) string {
+    fmt.Println("entering:", s)
+    return s
+}
+
+func un(s string) {
+    fmt.Println("leaving:", s)
+}
+
+func a() {
+    defer un(trace("a"))
+    fmt.Println("in a")
+}
+```
+
+## Data
+
+### Allocation with new
+- `new(T)` allocates zeroed storage for new item of type T
+- Returns `*T`
+- Returns memory address of newly allocated zero value
+
+```go
+p := new(int)   // p is *int, points to zeroed int
+```
+
+### Constructors and Composite Literals
+```go
+func NewFile(fd int, name string) *File {
+    if fd < 0 {
+        return nil
+    }
+    return &File{fd: fd, name: name}
+}
+```
+
+### Allocation with make
+- `make(T, args)` creates slices, maps, and channels only
+- Returns initialized (not zeroed) value of type T (not *T)
+
+```go
+make([]int, 10, 100)   // slice: len=10, cap=100
+make(map[string]int)   // map
+make(chan int, 10)     // buffered channel
+```
+
+### Arrays
+- Arrays are values, not pointers
+- Passing array to function copies the entire array
+- Array size is part of its type
+
+### Slices
+- Hold references to underlying array
+- Can grow dynamically with `append`
+- Passing slice passes reference
+
+### Maps
+- Hold references to underlying data structure
+- Passing map passes reference
+- Zero value is `nil`
+
+### Printing
+- `%v` - default format
+- `%+v` - struct with field names
+- `%#v` - Go syntax representation
+- `%T` - type
+- `%q` - quoted string
+
+## Initialization
+
+### Constants
+- Created at compile time
+- Can only be numbers, characters, strings, or booleans
+
+### init Function
+- Each source file can have `init()` function
+- Called after package-level variables initialized
+- Used for setup that can't be expressed as declarations
+
+```go
+func init() {
+    // initialization code
+}
+```
+
+## Methods
+
+### Pointers vs. Values
+- Value methods can be invoked on pointers and values
+- Pointer methods can only be invoked on pointers
+
+Rule: Value methods can be called on both values and pointers, but pointer methods should only be called on pointers (though Go allows calling on addressable values).
+
+```go
+type ByteSlice []byte
+
+func (slice ByteSlice) Append(data []byte) []byte {
+    // ...
+}
+
+func (p *ByteSlice) Append(data []byte) {
+    slice := *p
+    // ...
+    *p = slice
+}
+```
+
+## Interfaces and Other Types
+
+### Interfaces
+- A type implements an interface by implementing its methods
+- No explicit declaration of intent
+
+### Type Assertions
+```go
+value, ok := str.(string)
+```
+
+### Type Switches
+```go
+switch v := value.(type) {
+case string:
+    // v is string
+case int:
+    // v is int
+}
+```
+
+### Generality
+- If a type exists only to implement an interface and will never have exported methods beyond that interface, there's no need to export the type itself
+
+## The Blank Identifier
+
+### Unused Imports and Variables
+```go
+import _ "net/http/pprof"  // Import for side effects
+```
+
+### Interface Checks
+```go
+var _ json.Marshaler = (*RawMessage)(nil)
+```
+
+## Embedding
+
+### Composition, not Inheritance
+```go
+type ReadWriter struct {
+    *Reader  // *bufio.Reader
+    *Writer  // *bufio.Writer
+}
+```
+
+## Concurrency
+
+### Share by Communicating
+- Don't communicate by sharing memory; share memory by communicating
+- Use channels to pass ownership
+
+### Goroutines
+- Cheap: small initial stack
+- Multiplexed onto OS threads
+- Prefix function call with `go` keyword
+
+### Channels
+- Allocate with `make`
+- Unbuffered: synchronous
+- Buffered: asynchronous up to buffer size
+
+```go
+ci := make(chan int)            // unbuffered
+cj := make(chan int, 0)         // unbuffered
+cs := make(chan *os.File, 100)  // buffered
+```
+
+### Channels of Channels
+```go
+type Request struct {
+    args        []int
+    f           func([]int) int
+    resultChan  chan int
+}
+```
+
+### Parallelization
+```go
+const numCPU = runtime.NumCPU()
+runtime.GOMAXPROCS(numCPU)
+```
+
+## Errors
+
+### Error Type
+```go
+type error interface {
+    Error() string
+}
+```
+
+### Custom Errors
+```go
+type PathError struct {
+    Op   string
+    Path string
+    Err  error
+}
+
+func (e *PathError) Error() string {
+    return e.Op + " " + e.Path + ": " + e.Err.Error()
+}
+```
+
+### Panic
+- Use for unrecoverable errors
+- Generally avoid in library code
+
+### Recover
+- Called inside deferred function
+- Stops panic sequence
+- Returns value passed to panic
+
+```go
+func server(workChan <-chan *Work) {
+    for work := range workChan {
+        go safelyDo(work)
+    }
+}
+
+func safelyDo(work *Work) {
+    defer func() {
+        if err := recover(); err != nil {
+            log.Println("work failed:", err)
+        }
+    }()
+    do(work)
+}
+```
+
+## A Web Server Example
+
+```go
+package main
+
+import (
+    "fmt"
+    "log"
+    "net/http"
+)
+
+type Counter struct {
+    n int
+}
+
+func (ctr *Counter) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+    ctr.n++
+    fmt.Fprintf(w, "counter = %d\n", ctr.n)
+}
+
+func main() {
+    ctr := new(Counter)
+    http.Handle("/counter", ctr)
+    log.Fatal(http.ListenAndServe(":8080", nil))
+}
+```
+