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Error handling - Core helpers

This page lists all error handling operations available in the core package of lo.

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  • Validate​

    error-handlingcore
    🧩 Source📚 GoDoc🎮 Try on Go Playground

    Creates an error when a condition is not met; returns nil when it is.

    slice := []string{"a"}

    err := lo.Validate(len(slice) == 0, "Slice should be empty")
    // error("Slice should be empty")

    err := lo.Validate(len(slice) == 0, "Slice should be empty but contains %v", slice)
    // error("Slice should be empty but contains [a]")
    Similar:
    assertmustxtryorxtryx
    Prototype:
    func Validate(ok bool, format string, args ...any) error

  • MustX​

    error-handlingcore
    🧩 Source📚 GoDoc🎮 Try on Go Playground

    Panics if err is an error or false, returning successful values otherwise. Variants cover functions returning 0 to 6 values.

    // returns 10, panics if err is not nil
    v := lo.Must(strconv.Atoi("10"))

    // panics with custom message
    lo.Must0(fmt.Errorf("boom"), "failed to parse")

    // panics if myFunc returns an error
    func myFunc() (int, string, float64, bool, error) { ... }
    a, b, c, d := lo.Must4(myFunc())
    Variant:
    must
    Similar:
    asserterrorsastrycatchtryorxtrywitherrorvaluetryxvalidate
    Prototypes:
    func Must[T any](val T, err any, messageArgs ...any) T
    func Must0(err any, messageArgs ...any)
    func Must1[T any](val T, err any, messageArgs ...any) T
    func Must2[T1, T2 any](val1 T1, val2 T2, err any, messageArgs ...any) (T1, T2)
    func Must3[T1, T2, T3 any](val1 T1, val2 T2, val3 T3, err any, messageArgs ...any) (T1, T2, T3)
    func Must4[T1, T2, T3, T4 any](val1 T1, val2 T2, val3 T3, val4 T4, err any, messageArgs ...any) (T1, T2, T3, T4)
    func Must5[T1, T2, T3, T4, T5 any](val1 T1, val2 T2, val3 T3, val4 T4, val5 T5, err any, messageArgs ...any) (T1, T2, T3, T4, T5)
    func Must6[T1, T2, T3, T4, T5, T6 any](val1 T1, val2 T2, val3 T3, val4 T4, val5 T5, val6 T6, err any, messageArgs ...any) (T1, T2, T3, T4, T5, T6)

  • TryX​

    error-handlingcore
    🧩 Source📚 GoDoc🎮 Try on Go Playground

    Calls a function and returns false in case of error or panic. Variants cover callbacks returning 0 to 6 values.

    ok := lo.Try(func() error {
        // return an error to mark failure
        return fmt.Errorf("boom")
    })
    // ok == false

    ok = lo.Try0(func() {
        // panics are caught and return false
        panic("boom")
    })
    // ok == false

    ok = lo.Try2(func() (int, error) {
        return 42, nil
    })
    // ok == true
    Variant:
    try
    Similar:
    asserterrorsasmustxtrycatchtryorxtrywitherrorvaluevalidate
    Prototypes:
    func Try(callback func() error) bool
    func Try0(callback func()) bool
    func Try1(callback func() error) bool
    func Try2[T any](callback func() (T, error)) bool
    func Try3[T, R any](callback func() (T, R, error)) bool
    func Try4[T, R, S any](callback func() (T, R, S, error)) bool
    func Try5[T, R, S, Q any](callback func() (T, R, S, Q, error)) bool
    func Try6[T, R, S, Q, U any](callback func() (T, R, S, Q, U, error)) bool

  • TryOrX​

    error-handlingcore
    🧩 Source📚 GoDoc🎮 Try on Go Playground

    Like Try, but returns provided fallback values in case of error; also returns a success flag. Variants cover callbacks returning 1 to 6 values.

    value, ok := lo.TryOr(func() (int, error) {
        return 0, fmt.Errorf("boom")
    }, 123)
    // value == 123, ok == false

    value, ok = lo.TryOr(func() (int, error) {
        return 42, nil
    }, 0)
    // value == 42, ok == true
    Variant:
    tryor
    Similar:
    asserterrorsasmustxtrycatchtrywitherrorvaluetryxvalidate
    Prototypes:
    func TryOr[A any](callback func() (A, error), fallbackA A) (A, bool)
    func TryOr1[A any](callback func() (A, error), fallbackA A) (A, bool)
    func TryOr2[A, B any](callback func() (A, B, error), fallbackA A, fallbackB B) (A, B, bool)
    func TryOr3[A, B, C any](callback func() (A, B, C, error), fallbackA A, fallbackB B, fallbackC C) (A, B, C, bool)
    func TryOr4[A, B, C, D any](callback func() (A, B, C, D, error), fallbackA A, fallbackB B, fallbackC C, fallbackD D) (A, B, C, D, bool)
    func TryOr5[A, B, C, D, E any](callback func() (A, B, C, D, E, error), fallbackA A, fallbackB B, fallbackC C, fallbackD D, fallbackE E) (A, B, C, D, E, bool)
    func TryOr6[A, B, C, D, E, F any](callback func() (A, B, C, D, E, F, error), fallbackA A, fallbackB B, fallbackC C, fallbackD D, fallbackE E, fallbackF F) (A, B, C, D, E, F, bool)

  • TryWithErrorValue​

    error-handlingcore
    🧩 Source📚 GoDoc🎮 Try on Go Playground

    Runs a function and returns the error value (panic or error) along with a boolean indicating success.

    err, ok := lo.TryWithErrorValue(func() error { panic("error") })
    // err == "error", ok == false
    Similar:
    asserterrorsasmustxtrycatchtrycatchwitherrorvaluetryorxtryxvalidate
    Prototype:
    func TryWithErrorValue(callback func() error) (errorValue any, ok bool)

  • TryCatch​

    error-handlingcore
    🧩 Source📚 GoDoc🎮 Try on Go Playground

    Calls the catch function when the callback errors or panics.

    caught := false
    lo.TryCatch(func() error { panic("error") }, func() { caught = true })
    // caught == true
    Similar:
    asserterrorsasmustxtrycatchwitherrorvaluetryorxtrywitherrorvaluetryxvalidate
    Prototype:
    func TryCatch(callback func() error, catch func())

  • TryCatchWithErrorValue​

    error-handlingcore
    🧩 Source📚 GoDoc🎮 Try on Go Playground

    Calls the catch function with the error value when the callback errors or panics.

    lo.TryCatchWithErrorValue(
        func() error {
            panic("error")
        },
        func(val any) {
            fmt.Println(val)
        },
    )
    Similar:
    asserterrorsasmustxtrycatchtryorxtrywitherrorvaluetryxvalidate
    Prototype:
    func TryCatchWithErrorValue(callback func() error, catch func(any))

  • ErrorsAs​

    error-handlingcore
    🧩 Source📚 GoDoc🎮 Try on Go Playground

    A generic wrapper around errors.As that returns the typed error and a boolean indicating success.

    if rateLimitErr, ok := lo.ErrorsAs[*RateLimitError](err); ok {
        // handle
    }
    Variant:
    erroras
    Similar:
    assertmustxtrycatchtrycatchwitherrorvaluetryorxtrywitherrorvaluetryxvalidate
    Prototype:
    func ErrorsAs[T error](err error) (T, bool)

  • Assert​

    error-handlingcore
    🧩 Source📚 GoDoc🎮 Try on Go Playground

    Does nothing when condition is true; otherwise panics.

    // Base variant with optional message
    age := 12
    lo.Assert(age >= 15, "user age must be >= 15")
    // panics: "user age must be >= 15"

    // Without message - panics with default message
    x := -1
    lo.Assert(x > 0)
    // panics: "assertion failed: condition is not true"

    // Formatted variant with custom message
    age = 12
    lo.Assertf(age >= 15, "user age must be >= 15, got %d", age)
    // panics: "user age must be >= 15, got 12"

    // When condition is true - no panic
    age = 20
    lo.Assert(age >= 15, "user age must be >= 15")
    // continues normally

    Custom handler

    Replace lo.Assert and lo.Assertf with your own statement:

    lo.Assertf = func(condition bool, format string, args ...any) {
    		if !condition {
    			  panic(fmt.Errorf("%s: %s", "customErr", fmt.Sprintf(format, args...)))
    		}
    }
    Variant:
    assertf
    Similar:
    errorsasmustxtrycatchtryorxtrywitherrorvaluetryxvalidate
    Prototypes:
    func Assert(condition bool, message ...string)
    func Assertf(condition bool, format string, args ...any)