Error map
assignment mismatch: 1 variable but f returns 2 values Go: assignment mismatch: 1 variable but os.Open returns 2 values
Go · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
Go: listen tcp :8080: bind: address already in use
The port your Go server wants is already taken by another process (or a previous instance of your app).
Go: accept tcp [::]:8080: accept4: too many open files / open x: too many open files
The process reached its file-descriptor limit — usually leaked connections, files or response bodies.
Go: ./main.go:5:2: "os" imported and not used
The file imports a package that no code in that file uses; Go treats this as a compile error, not a warning.
Go: ./main.go:12:2: undefined: handler
The compiler cannot find an identifier — a typo, a missing import, or it lives in another file/package that wasn't built.
Go: ./main.go:18:1: missing return
A function with a return type can reach its end without a return statement on some path.
Go: ./main.go:9:6: no new variables on left side of :=
`:=` declares variables, but all names on the left already exist in the same scope.
Go: cannot assign to struct field users["bob"].Age in map
Map values are not addressable, so you cannot modify a field of a struct stored directly in a map.
Go: invalid operation: a + b (mismatched types int and float64)
You combined two values of different types; Go never converts numeric types implicitly.
Go: cannot use "5" (untyped string constant) as int value in argument to f
A value's type is not assignable to the type required by the variable, parameter or return value.
Go: not enough arguments in call to f have (int) want (int, string)
A function was called with fewer or more arguments than it declares.
Go: runtime.main_main·f: function main is undeclared in the main package
The package is named `main` but contains no `func main()`, or you tried to build a library as an executable.
Go: cannot refer to unexported name pkg.helper (undefined: pkg.helper)
You used a lowercase (unexported) identifier from another package; only capitalised names are visible outside their package.
Two steps away (19)
Docker: Bind for 0.0.0.0:80 failed: port is already allocated
Another container or host process already publishes that host port.
Error response from daemon: network X not found
The container or Compose project refers to a Docker network that doesn’t exist (any more).
Error response from daemon: Pool overlaps with other one on this address space
Docker tried to create a network whose subnet clashes with an existing Docker network (or a VPN/host route).
driver failed programming external connectivity on endpoint: iptables: No chain/target/match by that name
Docker’s iptables rules were wiped (firewalld/ufw reload, iptables flush) while Docker was running, so it can’t publish ports.
Go: cannot find package "github.com/pkg/errors" in any of: /usr/local/go/src/github.com/pkg/errors (from $GOROOT) /go/src/github.com/pkg/errors (from $GOPATH)
Go could not locate an imported package — it is not downloaded, the module is not initialised, or GOPATH mode is in effect.
Go: panic: assignment to entry in nil map
You wrote to a map that was declared but never initialised.
Go: declared and not used: x / "fmt" imported and not used
Go refuses to compile code with unused local variables or unused imports.
Go: cannot use &Dog{} (value of type *Dog) as Animal value: *Dog does not implement Animal (missing method Speak)
A type was used as an interface but lacks a method or has it with a different signature or receiver type.
Go: ./main.go:8:2: syntax error: unexpected newline, expected comma or )
The parser met a line break where it needed more tokens, usually a missing trailing comma in a multi-line literal or a misplaced…
Go: package app/models imports app/utils imports app/models: import cycle not allowed
Two or more packages import each other directly or indirectly, which Go forbids.
Go: fatal error: concurrent map writes
Two goroutines wrote to the same map at the same time; the runtime detects it and aborts the program (not recoverable).
Go: fatal error: concurrent map read and map write
One goroutine read from a map while another wrote to it; the runtime aborts.
Go: Get "https://api.example.com": context deadline exceeded (Client.Timeout exceeded while awaiting headers)
An operation did not finish before its context deadline or HTTP client timeout.
Rust: error[E0308]: mismatched types — expected `X`, found `Y`
A value’s type doesn’t match what the context expects — common with &str vs String, Option/Result vs plain values, and integer ty…
Go: sql: no rows in result set
`QueryRow(...).Scan(...)` found no row for the query.
COPY failed: file not found in build context / "/app/x": not found
The Dockerfile COPY refers to a path outside the build context, excluded by .dockerignore, or relative to the wrong directory.
failed to solve: process "/bin/sh -c ..." did not complete successfully: exit code: 1
A RUN step in your Dockerfile failed. The real error is printed in the lines just above this message.
failed to solve: failed to read dockerfile: open Dockerfile: no such file or directory
docker build can’t find a Dockerfile in the build context you passed.
Go: json: cannot unmarshal string into Go struct field User.age of type int
The JSON value's type does not match the Go field type (string vs number, object vs array).
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